JP2000133884A - Quantum well structure light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an n-type light-emitting layer of quantum well structure which is superior in emission intensity and monochromaticity by a method, wherein the conductor of a terminal well layer is so formed in potential as to be curved and protrudes downward on a low potential side toward the Fermi level. SOLUTION: A single-quantum well structure has a structure, where a well layer 11 is pinched between a barrier layer 10 and an interposing layer 12 to form a light-emitting layer. The light-emitting layer 1a is pinched between an n-type clad layer 13 and a p-type clad layer 14 to form a light-emitting section 1. That is, the well layer 11 serves as a terminal well layer 11a, and the interposing layer 12 is inserted between the terminal well layer 11a and the p-type clad layer 14. At this point, a conductor 16 is formed curved protruding downward to form a low potential section 18, only in the inner region of the terminal well layer 11a near its junction interface 15a with the n-type interposition layer 12. With this setup, a light-emitting layer of quantum well structure formed of III nitride semiconductor and superior in monochromaticity can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for forming a pn junction type DH quantum well structure light emitting device using a quantum well structure made of a group III nitride semiconductor crystal as a light emitting layer. The present invention relates to a technique for forming a light emitting layer having a quantum well structure that emits light with excellent brightness and monochromaticity.

[0002]

2. Description of the Related Art Light-emitting diodes (LEDs) that emit short-wavelength visible light such as a blue band or a green band that have been put into practical use
Most of light emitting devices such as n-type gallium indium nitride (GaαIn _1- α) which is a kind of group III nitride semiconductor
N: 0 ≦ α ≦ 1) as a light emitting layer (active layer). GaαIn ₁ -αN has an indium composition ratio (= 1−1).
α) Depending on how it is provided, at room temperature, a convenient bandgap for emitting short-wavelength visible light or near-ultraviolet light ranging from about 2.0 electron volts (eV) to about 3.4 eV. This is the reason (Patent Application Publication No. 3 of 1980)
No. 834).

A conventional light emitting portion has a so-called pn junction type double hetero structure in which a light emitting layer made of GaαIn ₁ -αN is sandwiched between n-type and p-type cladding layers.
Hetero: DH) structure (Jpn. J. Appl. Phys., Vol . 3).
4 , Part2, No. 10B (1995), L133
2-L1335). On the other hand, if the conventional example of the crystal structure of the light emitting layer is omitted, there is an example in which the light emitting layer is formed from a single layer of GaαIn ₁ -αN having a uniform indium composition (Japanese Patent Laid-Open No. 9-36430). See specification). Further, when viewed stacked structure, a single quantum well (S ingle
Q uantum W ell: SQW) structure or a multiple quantum well (M ulti Q uantum W ell: M
A technique comprising a QW) structure is disclosed (see Japanese Patent Application Laid-Open No. 9-36430).

[0004] If the light emitting layer is formed of an SQW or MQW structure, there is an advantage that light emission with particularly excellent monochromaticity can be obtained. This is because a laser diode (LD) has an advantage of lowering the oscillation threshold (Yasuharu Suematsu, “Optical Device” (Corona Co., Ltd., May 15, 1997, first edition) 8th print), page 63).

FIG. 9 schematically shows an energy band structure of a conventional SQW which is also a component of the MQW. SQW
Are basically layers 010, 011 exhibiting a barrier action,
It is configured with a junction with a well layer 012 as a light emitting layer sandwiched therebetween. In forming a light emitting layer having a quantum well structure, it is a conventional example that the thickness of a barrier layer is substantially the same (see Japanese Patent Application Laid-Open No. 9-36422). Similarly, there is known an example in which a well layer is formed of Ga _0.93 In _0.07 N having substantially the same layer thickness including a well layer (terminating well layer) forming a terminal of a quantum well structure (Japanese Patent Laid-Open No. 9-36423). Gazette).

FIG. 10 shows a rectangular potential configuration in the SQW structure shown in FIG. The barrier layers 010 and 011 are formed by the forbidden band width 013 of the well layer 012.
It is usually made of a material having a larger band gap 014, 015. On the conduction band 017 side of the potential well portion 016 in the region where the well layer 012 is arranged,
Quantum levels 019, 02 maintaining a constant level from the conduction band edge
0 has occurred. Also, on the valence band 018 side, quantum levels 021 and 022 maintaining a constant level from the valence band edge.
Has occurred. Due to the generation of the quantum levels 019 to 022, the transition energies 023 and 024 are changed to the well layer 012.
Is larger than the forbidden band width 013 (see “Optical Device”, page 63). Therefore, the theory teaches that the wavelength of light emitted from the quantum well structure shifts to a shorter wavelength side than the wavelength corresponding to the band gap inherent to the material forming the well layer.

A conventional III having a light emitting layer of a quantum well structure
In the light emitting device having the group III nitride semiconductor DH structure, the potential configuration of the light emitting portion is, as illustrated in FIG.
In general, it has a rectangular potential configuration which is symmetrical with respect to the center line 12 (see Japanese Patent Application Laid-Open No. 8-11612).
8 and JP-A-9-8412). Alternatively, it has a potential configuration in which the levels of the conduction band and the valence band uniformly and linearly change (Ma
t. Res. Soc. Symp. Proc. , Vol.
449 (1997), pp. 1167-1172). However, on the other hand, even from such a general rectangular potential well structure, contrary to the theoretical result pointed out by quantum mechanical theory, the regular (III) of the group III nitride semiconductor constituting the well layer (light emitting layer) is used. 2. Description of the Related Art A nitride semiconductor light emitting device that emits light with energy smaller than the original band gap energy is known (JP-A-8-316528 and EUROPEAN PATENT APPLICATION EP-0 716).
457 A2).

[0008]

In a light emitting layer having a quantum well structure in which GaαIn ₁ -αN is used as a well layer, one conventional technique used for controlling an emission wavelength is an indium composition ratio (= 1). −α).
For example, when it is desired to increase the emission wavelength, GaαIn ₁₋ α having a relatively large indium composition ratio is used.
Measures will be taken to make N a well layer. This is because as the indium composition ratio increases, the band gap of GaαIn ₁ -αN becomes smaller, and the emission wavelength becomes longer accordingly (see Japanese Patent Publication No. 55-3834).

However, in order to obtain GaαIn ₁ -αN having a high indium composition ratio of, for example, about 0.4 to about 0.5, it is necessary to set the film forming temperature to a low temperature of about 600 ° C. (Materials Letters,
35 (1985), pages 85-89). It is known that GaαIn ₁ -αN formed at a low temperature of about 500 ° C. has poor crystallinity (“Journal of the Institute of Electronics, Information and Communication Engineers”,
Vol. 76, No. 9 (September 1993), 913-
917). The superiority of the group III nitride semiconductor crystal layer constituting the well layer is reflected in the level of the light emission intensity of the light emitting element. Constituting the well layer from GaαIn ₁ -αN having poor crystallinity hinders obtaining a quantum structure light-emitting layer that emits light with excellent intensity. That is, one of the problems in the prior art is that it is difficult to obtain a light emitting element having a quantum well structure with high luminance.

[0010] In the quantum well structure, a quantum level resulting in an increase in the transition energy of carriers is generated in the well layer (for example, see Japanese Patent Application Laid-Open No. 9-8412). Therefore,
In order to obtain the same emission wavelength, it is necessary to form the well layer from GaαIn ₁ -αN having a higher indium composition ratio as compared with the case where the light-emitting layer is formed from a single layer. As mentioned above, to achieve a high indium composition ratio,
The crystallinity becomes worse as the GaαIn ₁ -αN crystal formed at a lower temperature. That is, Gaα having a high indium composition ratio
At present, short-wavelength visible light such as a green band, which is excellent in intensity, cannot be conveniently obtained from a quantum well structure light emitting layer composed of In ₁ -αN.

On the other hand, following another prior art, the quantum well structure which emits light of a longer wavelength than the corresponding forbidden band gap of the group III nitride semiconductor constituting the well layer is changed from the light emitting layer to the light emitting layer. (Japanese Patent No. 278069)
1), it is necessary to invent a potential configuration different from an unreasonable rectangular potential well structure which cannot theoretically achieve a longer wavelength of light emission. The first problem to be solved by the present invention is also present here. GaαIn ₁ -αN having a relatively low indium composition ratio, which has an advantage of emitting light with excellent monochromaticity, is simple in crystal growth, and has excellent crystallinity. It is another object of the present invention to provide a structure of a quantum well structure that can easily and stably emit light in a blue-green band or a green band. In particular, it is an object of the present invention to provide a configuration of a quantum well structure having a suitable potential structure from the viewpoint of a band structure.

The second object of the present invention is to solve the conventional problem that the emission intensity is sensitively changed depending on the crystallinity of GaαIn ₁ -αN constituting the well layer.
For example, it is to clarify the requirements that the well layer of the quantum well structure should have in order to provide a blue-green band or higher-intensity light emission from the viewpoint of a crystalline material. An object of the present invention is to solve the above-mentioned main problems and to provide a light-emitting element having a light-emitting layer having a quantum well structure made of a group III nitride semiconductor, which is excellent in light emission intensity and monochromaticity of light emission. Is to do.

[0013]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned problems of the prior art and provides a quantum well having an n-type light emitting layer having a quantum well structure excellent in both emission intensity and monochromaticity. It is made for the purpose of providing a structural light emitting device. In particular, the invention described in claim 1 makes sense to bring about emission of energy lower than the forbidden band of the semiconductor material constituting the well layer (active layer), which was unclear in the prior art, and A light emitting device having a light emitting layer having a single or multiple quantum well structure including a convenient band structure is presented. Another object of the present invention is to describe a junction structure relating to a well layer that can provide the band structure conveniently.

That is, the invention according to claim 1 includes an n-type light emitting layer formed on one surface of a crystal substrate and sandwiched between n-type and p-type cladding layers made of a group III nitride semiconductor crystal layer. Further, in a light emitting device having a pn junction type double hetero (DH) structure, the n-type light emitting layer has a single or multiple quantum well structure, and a well layer (termination well layer) constituting an end of the quantum well structure. ) And the p-type cladding layer, an intervening layer made of an n-type group III nitride semiconductor is disposed, and the terminal well layer is formed in a region near a junction interface between the n-type intervening layer and the terminal well layer. An indium (In) -containing n-type group III nitride semiconductor having a potential configuration in which a conduction band of the terminal well layer is bent downward and convex toward a lower potential side toward a Fermi level. Consisting of crystal layers It is characterized by.

According to a second aspect of the present invention, in the first aspect of the present invention, the terminal well layer faces the n-type intervening layer with the n-type intervening layer sandwiching the terminal well layer. It is characterized by being sandwiched between a barrier layer.

According to a third aspect of the present invention, in the second aspect, the n-type barrier layer has substantially the same composition and the same thickness as the n-type intervening layer. I have.

The fourth aspect of the present invention relates to a terminal well layer including a potential configuration that is advantageous for increasing the emission wavelength. That is, claim 4
In the invention described in (2), in the invention described in (2) or (3), the terminal well layer directs the valence band of the terminal well layer to the Fermi level in a region near a junction interface with the n-type barrier layer. And has a low potential region bent upward and convex.

The invention described in claim 5 is the same as the claim 4.
In the invention described in the above, it is possible to provide light emission of a longer wavelength than corresponding to the band gap of the semiconductor material forming the well layer,
This is an invention that conveniently defines the size of the bending of the band.
That is, in the invention according to claim 5, the terminal well layer is
The energy difference (ΔEc = | Eco−Ec |) between the original potential level (Eco) of the conduction band and the low potential end (Ec) dropped to the Fermi level side, and the original potential level (Evo) of the valence band ) And the energy difference (ΔEv = | Evo−Ev |) between the low potential end (Ev) dropped to the Fermi level side, and the total energy difference (ΔEc + ΔEv) is 0.4 electron volts (eV) or more. It is characterized by having a bending of the conduction band and the valence band.

Further, the invention according to claim 6 provides the invention according to claim 4.
In the invention according to the fifth aspect, in particular, the invention provides a configuration for obtaining light emission excellent in monochromaticity from a light emitting layer having a multiple quantum well structure. That is, in the invention according to claim 6, in the invention according to claim 4 or 5, the n-type light emitting layer has a multiple quantum well structure, and the layer thickness of the terminal well layer is the sum of the above-mentioned total. Energy difference (ΔEc + ΔE
v) is larger than the total energy difference of the other well layers.

The invention described in claim 7 is the first invention.
In the invention according to any one of Items 1 to 6, excellent in monochromaticity,
In addition, the present invention particularly provides an advantage in forming a terminal well layer that is convenient for increasing the wavelength of light emission. That is, in the invention according to claim 7, in the invention according to any one of claims 1 to 6, the n-type light-emitting layer has a multiple quantum well structure, and the thickness of the terminal well layer is changed to another thickness. It is characterized in that the thickness is not more than the thickness of the well layer.

The invention described in claim 8 is the first invention.
In the inventions of (1) to (7), the present invention provides requirements for forming a terminal well layer capable of increasing emission intensity. That is, in the invention described in claim 8, in the invention described in any one of claims 1 to 7, the terminal well layer includes a main phase having an indium composition ratio (= X) of 0.3 or less; Is a multiphase n-type gallium indium nitride (Ga _1−x In _x N: 0 ≦ X ≦) having a different indium composition ratio and including a dependent phase having a strained layer in the junction boundary region with the main phase.
0.3).

The invention according to claim 9 is the invention according to claim 8
In the invention described in (1), the requirement that the well layer should have in order to further increase the emission intensity is presented. That is, the invention of claim 9 is the invention according to claim 8, the termination well layer made from the multi-phase structure, the oxygen atom concentration in 5 × 10 ¹⁷ cm ^-3 to 5 × 10 ²⁰ cm ^{- It} is characterized by being made of an n _-type Ga _1-x In _x N (0 ≦ X ≦ 0.3) crystal whose number is ³ or less.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment according to the first aspect of the present invention will be described in the case where the quantum well structure is a single quantum well (SQW) structure. FIG. 1 illustrates an energy band structure of a light emitting unit 1 having a pn junction type DH structure of an SQW structure 1b having a structure in which a barrier layer 10, a well layer 11, and an intervening layer 12 are sequentially stacked. The SQW structure 1b according to the present invention includes one barrier (barrier: barr).
ier) layer 10 and one intervening layer 12 so as to sandwich one well layer 11.
a is formed. The light emitting layer 1a includes the n-type cladding layer 1
3 and the p-type cladding layer 14 to constitute the light emitting section 1. In the SQW structure including the single well layer, the single well layer 11 is the terminal well layer 11a. The feature of the quantum well structure of the present invention is that the terminal well layer 11a
And an intermediate layer 12 is inserted between the p-type cladding layer 14 and the p-type cladding layer 14. That is, in the present invention, the termination well layer 11a
Is not directly bonded to the p-type crystal layer.

FIG. 2 shows a quantum well structure of the first embodiment according to the first aspect of the present invention.
It is a figure for explaining the case where it is a QW) structure based on an energy band structure. As in the case of the SQW structure, an intermediate layer 1 is provided between the terminal well layer 11a and the p-type cladding layer 14.
2 is inserted. This MQW structure 1d
The light emitting layer 1a is sandwiched between the n-type and p-type cladding layers 13 and 14 to form the light emitting section 1. The well layer 11 which joins the intervening layer 12 and forms the final end of the MQW structure 1d
a is a terminal well layer. The well layer adjacent to the intervening layer 12 next to the terminal well layer 11a as the first proximity well layer is the second proximity well layer 11b. The well layers (11c to 11e in FIG. 2) arranged between the second proximity well layer 11b and the n-type cladding layer 13 are the second proximity well layers 1.
1b and subsequent well layers. These well layers 11a to 11
e and the barrier layer 10 are alternately layered to form a five-period MQW structure 1.
d is configured.

In FIG. 2, n-type and p-type cladding layers 1
3, 14 can be composed of n-type and p-type, for example, aluminum-gallium nitride mixed crystal (Al _Y Ga _1-Y N: 0 ≦ Y ≦ 1). It is a conventional means for creating a quantum level that the well layers 11a to 11e are made of a semiconductor material having a smaller band gap than the barrier layer 10 and the intervening layer 12. In addition to nitrogen, other Group V elements such as arsenic (As) and phosphorus (P) are used as constituent elements. For example, gallium arsenide mixed crystal (GaN _1-Y As _Y : 0 <Y <1) or phosphorus It is also possible to form the well layer from an n-type group III nitride semiconductor material such as gallium oxynitride (GaN _1-Z P _Z : 0 <Z <1). However, by containing indium (In) as a constituent element, an indium-containing group III nitride semiconductor material that more suitably provides a band gap suitable for emitting short-wavelength visible light, particularly Ga _1-X In _X N It is composed of a mixed crystal and prefers a well layer.

The well layer and the barrier layer exhibit n-type conduction.
It is preferable to use a group III nitride semiconductor crystal layer.
The well layer and the barrier layer are made of a group IV element such as silicon (Si) or tin (Sn), or a group VI element such as sulfur (S) or selenium (Se).
And the like can be constituted by an n-type group III nitride semiconductor crystal layer doped with an n-type impurity such as However, in order to avoid inadvertent formation of levels due to impurities, in the present invention, it is most preferable to form the well layer from an undoped and high-purity Ga _1-x In _x N mixed crystal. The barrier layer is
In particular, it is preferable to use an n-type crystal layer having excellent conductivity.

In the present invention, the layer thickness suitable for functioning as a barrier layer and a well layer is not particularly specified. Transfer of carrier (transport)
A suitable layer thickness for the barrier layer exhibiting a barrier effect on the light emission and the well layer responsible for light emission is Kronig-Penny (Kr
(K. Seeger, "Physics of Semiconductors (1)" (Yoshioka Shoten, 199)
The first printing was issued on June 10, 2001), pages 12 to 21). In general, the barrier layer generally has a layer thickness of about 10 to 20 nm that can exhibit a tunnel effect. Generally, the thickness of the well layer is generally 10 nm or less. The constituent requirements of the well layer, the barrier layer, and the intervening layer having the MQW structure are the same as those of forming the light emitting layer having the SQW structure. The thicknesses of the barrier layers constituting the light emitting layer having the MQW structure need not be the same. Similarly, there is no necessity to unify the thicknesses of the well layers constituting the MQW structure.

The intervening layer 12 is made of a group III nitride semiconductor material constituting the terminal well layer 11a, for example, having a larger band gap than n-type Ga _1-x In _x N. In particular, as described later, when the terminal well layer 11a is composed of a multiphase structure composed of a plurality of phases having different indium concentrations, the terminal well layer 11a is formed of a material having a main phase that mainly constitutes the terminal well layer 11a. It is made of a group III nitride semiconductor having a band gap. Further, the intervening layer 12 is transparent to short-wavelength light emitted from the well layer 11a, for example, Al _Y Ga ₁ -YN.
(0 ≦ y ≦ 1) It is preferable to constitute the material.
Intervening layer 12 is composed of an n-type crystal layer. The carrier concentration is less than about 5 × 10 ¹⁷ cm ^-3 , preferably 1 × 10 ¹⁷ cm ^-3
It is preferable to use a high-purity Group III nitride semiconductor material with a low carrier concentration of ^-3 or less. Approximate layer thickness, 5
0 nm or less, preferably 20 nm or less is suitable.

Since it is preferable that the intervening layer 12 be formed of a high-purity crystal layer with a low carrier concentration, if the layer thickness is unnecessarily thick, the forward voltage of the light emitting element will increase, and driving at a low voltage will occur. This causes inconvenience in obtaining a light emitting element with low possible power consumption. Conversely, if the intervening layer 12 is extremely thin, the continuity of the film is impaired, and the surface of the terminal well layer 11a cannot be covered with a uniform thickness. Insufficient for uniform generation. Therefore, it is preferable that the thickness of the intervening layer be 2 nm or more.

FIG. 3 is a diagram for explaining in more detail the energy band configuration near the junction interface of each layer of the light emitting section 1 having the light emitting layer 1a of the SQW structure 1b according to the first embodiment shown in FIG. Band diagram
gram). The band structure according to the first embodiment is characterized in that the conduction band 16 is bent downward to the Fermi level 17 only in the inner region of the terminal well layer 11a near the junction interface 15a with the n-type intervening layer 12. The low potential portion 18 is formed by bending.

FIG. 4 shows the MQ signal shown in FIG.
It is a band diagram corresponding to W structure 1d. SQ
Regardless of the W structure 1a and the MQW structure 1d, the feature of the band configuration according to the first embodiment is that the conduction band 1 is formed in the terminal well layer 11a near the junction interface 15a with the n-type intermediate layer 12.
6 is that the low potential portion 18 is particularly remarkably formed by the bending bent downward to the Fermi level 17 side.

As described above, in order to form the low potential region 18 in the conduction band 16, the composition must be changed sharply at the heterojunction interface 15a between the terminal well layer 11a and the n-type intermediate layer 12. Is required. For example, n-type Al
_The intervening layer 12 is formed from YGa _1-YN (0 ≦ Y ≦ 1).
N-type Ga _1-x In having a band gap smaller than that of the intermediate layer 12
_In the heterojunction system with the terminal well layer 11a composed of XN (0 <X ≦ 1), the atomic concentration of aluminum (Al) or indium (In) is the average concentration in a layer containing it as a constituent element. , The transition region width required to increase or decrease the concentration is about 20 nm or less, preferably about 15 nm.
Hereinafter, it is more preferable that the thickness be about 12 nm or less. The transition region width is determined by a general secondary ion mass spectrometry (S
It can be measured based on the analysis result of the distribution state of the element by IMS or Auger electron spectroscopy (AES). If the width of the transition region is within the above range, the necessary conditions for creating a low potential portion in the conduction band or the valence band can be made uniform.

Electrons 19 can be accumulated in the low potential region 18 of the conduction band 16 provided locally in the vicinity of the junction interface 15a between the intervening layer 12 and the terminal well layer 11a. If the low potential portion 18 is provided adjacent to the junction interface 15a with the p-type cladding layer 14 for supplying the electrons 19, and a storage region for the electrons 19 is provided, the positive potential has a shorter diffusion length than the electrons. There is an advantage that holes can be efficiently captured, and thus radiative recombination of electrons and holes can be effectively performed in the vicinity of the accumulation region.

The low potential portion 18 of the conduction band 16
Is not formed by a change in the potential at a uniform rate, but is formed by a sharp band bending in a very limited narrow region near the junction interface 15a with the intervening layer 12 and the terminal well layer 11a. ing. Therefore, carriers (electrons) localized in the minute region can behave as low-dimensional, for example, two-dimensional carriers. For this reason, there is also an advantage that a high-speed responsive quantum well structure light-emitting layer is provided with a high-speed carrier owing to a low-dimensional structure, and a high-speed responsiveness (response).

A second aspect according to the invention described in claim 2 of the present application
The arrangement relationship of the crystal layers shown in the embodiment is that the terminal well layer is n
Means to directly join to the intervening layer. That is, in the light emitting layer having the quantum well structure, it means that the terminal is constituted by the well layer. This arrangement is illustrated in FIGS. 1 and 2. The reason why the junction is made directly to the n-type intervening layer is that this junction effectively causes the conduction band to be bent in the terminal well layer. If the arrangement relationship of the present embodiment is summarized in relation to the arrangement of the n-type barrier layer constituting the quantum well structure together with the well layer, the terminal well layer is arranged between the n-type intermediate layer and the n-type barrier layer. (See FIGS. 1 and 2). S
In the QW structure, the n-type barrier layer can be substituted for the n-type cladding layer.

A third aspect according to the invention described in claim 3 of the present application.
The feature of forming the quantum well structure in the embodiment of the present invention is that the interposition layer 1 preferably exhibits n-type conduction.
2 and the n-type barrier layer 10 joined to the terminal well layer 11a
It consists of materials having substantially the same composition. For example, n-type and high-resistance Al _Y Ga _{1 -Y} N (0 ≦ Y ≦ 1)
, The n-type barrier layer 10 is made of Al _Y Ga having the same aluminum composition ratio (= Y).
_1-Y N (0 ≦ Y ≦ 1). Alternatively, Al _Y Ga ₁ -YN (0
≦ Y ≦ 1). Regarding the conductivity of the n-type barrier layer 10, it is preferable that the intervening layer 12 be formed of a high-purity, high-resistance crystal layer. It is preferable to use a group III nitride semiconductor crystal layer that is excellent in quality. Specifically, n
The carrier concentration of the barrier layer 10 is at least about 1 × 10 ¹⁶ cm ⁻³ or more, preferably about 1 × 10 ¹⁶ cm ⁻³ to secure conductivity.
It is preferably more than × 10 ¹⁷ cm ^-3 and about 1 × 10 ¹⁸ cm ^-3 or more. However, when the carrier concentration is 1 × 10 ¹⁹ cm
^If it exceeds ^-3 , on the contrary, the crystallinity of the n-type barrier layer 10 deteriorates. Therefore, the carrier concentration is preferably set to about 1 × 10 ¹⁹ cm ⁻³ or less.

The effect of this embodiment will be described by taking the SQW structure 1b shown in FIG. 1 as an example. If the intervening layer 12 and the n-type barrier layer 10 are made of substantially the same material, Layer 11a is provided with bonding surfaces 15a, 1
The stress applied from 5b can be made substantially uniform.
Under the situation where the applied stress is substantially equal, it is possible to more easily control the degree of band bending at the bonding interfaces 15a and 15b depending on the steepness at the interfaces.

Furthermore, when the intervening layer 12 and the n-type barrier layer 10 joined to the termination well layer 11a are made of a group III nitride semiconductor material having substantially the same thickness, the n-type barrier layer 10 and the intervening layer 12 The stress applied to the terminal well layer 11a from both sides can be equalized. This is advantageous in generating a uniformly bent band in the terminal well layer 11a. Substantially the same generally refers to a difference in thickness of less than ± 10%.

In the fourth embodiment according to the fourth aspect of the present invention, utilizing the technical means for determining the bending of the band substantially uniquely with the steepness of the bonding interface, the present invention is applied to the addition of the conduction band. To form a valence band bend. The band configuration according to the present embodiment will be described with reference to the band diagram of FIG. A feature of the band configuration according to the fourth embodiment is that a junction interface 1 between the terminal well layer 11a and the n-type barrier layer 10 is formed.
Only in the region near 5b, the low potential portion 21 is formed by bending the valence band 20 so as to protrude upward to the Fermi level 17 side. Further, as shown in the third embodiment, according to the configuration in which the terminal well layer 11a is sandwiched between the n-type intermediate layer 12 and the n-type barrier layer 10 having substantially the same composition and thickness, the conduction band 16 In addition to the above, the band bending can be conveniently formed on the valence band 20 side.

In the low potential portion 21 bent to the Fermi level 17 side, holes 22 that perform radiative recombination with electrons 19 can be effectively accumulated. This low potential portion 21
Is lower than the energy level of the original valence band 20, and the energy level of the holes 22 accumulated in this region is lower than the original. As described above, the energy level of the electrons 19 accumulated in the low potential portion 18 near the junction interface 15a with the intervening layer 12 is also low. Therefore, the transition energy 23 between the electron 19 and the hole 22 in such a band configuration is caused by the band gap 2 of the group III nitride semiconductor material forming the terminal well layer 11a.
It is smaller than 4. Therefore, the emission wavelength is equal to that of the terminal well layer 11.
A light having a wavelength longer than the wavelength corresponding to the band gap 24 of the group III nitride semiconductor material constituting a is provided.

As shown in FIG. 2, the degree of bending of the conduction band 16 in the well layer depends on the original potential level (Eco) 16 a of the conduction band 16 and the low potential end (Ec) dropped to the Fermi level 17 side. It is represented by an energy difference (ΔEc = | Eco−Ec |) 16c with respect to 16b. On the other hand, the original potential level (Ev
o) The energy difference (ΔEv) between 20a and the low potential end (Ev) 20b that has dropped to the Fermi level 17 side.
= | Evo-Ecv |) 20c, the valence band 20
The degree of fold is expressed. ΔEc (= 1) on the conduction band 16 side
6c) and the energy difference ΔEc + ΔEv, which is the sum of ΔEv (= 20c) on the valence band 20 side, is the total energy difference referred to in the present invention. For example, a value obtained by subtracting the total energy difference ΔEc + ΔEv from the regular band gap 24 of the semiconductor material forming the terminal well layer 11 a gives the transition energy 23.

In the fifth embodiment of the present invention, as described in claim 5 of the present application, the above total energy difference ΔEc +
From the well layer having ΔEv of 0.4 eV or more to the terminal well layer 1
1a. At least ΔEc + ΔEv is 0.4
This is because the terminal well layer 11a having eV or more provides an advantageous effect for increasing the emission wavelength. In order to make the total energy difference ΔEc + ΔEv 0.4 eV or more, the terminal well layer is sandwiched between the intervening layer and the barrier layer having substantially the same composition and thickness, and the stress is almost equally applied from both crystal layers to the terminal well layer. Is more preferable. If such prerequisites are prepared, the steepness of the bonding interface described later (edited by the Physical Society of Japan, “Physics and Application of Semiconductor Superlattice”, published by Baifukan Co., Ltd., first edition on September 30, 1986) 4 prints), 139
145), a well layer can be formed in which at least the total energy difference ΔEc + ΔEv is 0.4 eV or more.

If the degree of the "drop" of the band is significantly different for each well layer constituting the multiple quantum well (MQW) structure, a level formed in the low potential region in the well layer is added to the difference. It depends on the layer. Therefore, the transition energy of carriers is different for each well layer,
There is a disadvantage that light emission having different wavelengths is obtained for each well layer. In order to secure monochromatic light emission, in the sixth embodiment according to the invention described in claim 6 of the present application,
The configuration of the terminal well layer is further defined based on the total energy difference ΔEc + ΔEv. That is, in the sixth embodiment of the present invention, the terminal well layer having the multiple quantum well structure is configured with a well layer in which the total energy difference (ΔEc + ΔEv) is larger than the total energy difference of the other well layers. I do.

Referring to the band diagram of FIG. 4, the degree 25c of the “drop” of the potential of the conduction band 16 at the junction interface 15c of the second proximity well layer 11b with the barrier layer 10a is determined by the first The feature is that it is smaller than the depth 25a of the depression of the adjacent well layer 11a. Also, the degree 25d of the drop of the valence band 20 at the junction interface 15d with the barrier layer 10b is reduced by the first proximity well layer 11a.
The feature is that the degree of dip of the valence band 20 in the inside is smaller than 25b. In summary, the total energy difference (25c + 25d) in the second adjacent well layer 11b
) Is smaller than the total energy difference (corresponding to 25a + 25b) in the terminal well layer 11a. The carriers (electrons 19 and holes 22) are accumulated in the low potential portions 18 and 21 inside the terminal well layer 11a preferentially over the second adjacent well layer 11b, and the well layers 11c after the second adjacent well layer 11b are accumulated. This is because the accumulation region of the electrons 19 and the holes 22 due to the bending of the conduction band 16 is not internally included in the layers 11e to 11e.

In forming the light emitting layer from the MQW structure, an n-type barrier layer adjacent to the subsequent well layers 11c to 11e including the first adjacent well layer (terminal well layer) 11a and the second adjacent well layer 11b is provided. Is assumed to conform to the third embodiment, the region where electrons 19 as carriers for causing light emission accumulate is substantially one place in terms of potential.
I can concentrate on 8. On the other hand, the region where the holes 22 can be accumulated is also limited to the specific region 21. That is, since the carriers are confined to the specific potential regions 18 and 21 inside the terminal well layer 11a, the electrons 19 and the holes 22 having substantially constant energy can be used to cause radiative recombination. For this reason, light emission excellent in unity of emission wavelength, that is, monochromaticity is provided. If a low potential portion having substantially the same “dip” of the conduction band 16 and the valence band 20 is formed in each of the well layers 11c to 11e after the second proximity well layer 11b, the formed quantum level Also, there is an advantage that the light emission is substantially the same between the wells, and light emission with a uniform wavelength is provided. Ideally, there is no “drop” in the potential in the well layers after the second adjacent well layer.

In particular, in order to form a remarkable “drop” in the potential of the terminal well layer 11 a, the steepness of the composition at the junction interface with respect to the terminal well layer is improved. For example, if the transition distance of the indium atom concentration is 10 nm or less in the terminal well layer made of gallium nitride / indium mixed crystal, the above total energy difference (ΔEc + ΔEv) can be 0.4 eV or more. On the other hand, if a deep potential drop exceeding approximately 1 eV to 1.5 eV is formed, the emission wavelength becomes undesirably a long wavelength, and it becomes impossible to constantly emit short-wavelength visible light. For example, the forbidden band width at room temperature where a potential portion lower than the conduction band by about 1.7 eV is formed is about 3.1 eV.
When the terminal well layer is formed from the Ga _0.9 In _0.1 N crystal described above, infrared light having a wavelength exceeding about 800 nm is emitted.

In order to make the potential drop in the terminal well layer in the MQW structure larger than those in the other well layers, the steepness of the junction interface on both sides of the terminal well layer is determined by the other well layer. What is necessary is just to make it excellent compared with the case of. In order to intentionally cause a difference in the interface steepness, for example, there is a method of providing an interval in a film formation period, that is, a method of providing an opportunity to interrupt growth. According to the method of controlling the steepness of the junction interface by interrupting the growth, the steepness of the interface generally improves when the growth interruption time is extended. Without setting a growth suspension period,
When film formation is continuously performed, the steepness of the bonding interface becomes poor. For example, Ga _0.9 I on an n-type GaN barrier layer
When the n _0.1 N terminal well layer is continuously deposited, the transition distance of the indium atom concentration at the junction interface may well exceed 20 nm and reach about 40 nm to about 50 nm. Therefore, the steepness of the terminal well layer is reduced by adjusting the growth interruption time for the terminal well layer, and by not intentionally providing a film suspension time when forming another well layer. In comparison, it can be excellent.

Further, as described in the seventh embodiment of the present invention, in the structure of the MQW light emitting layer, particularly, the terminal well layer 11a is made of a material having a different layer thickness from the other well layers. This has the advantage that the emission wavelength can be easily changed. For example, if only the thickness of the terminal well layer 11a is simply made thicker than the other well layers without changing the group III nitride semiconductor material forming the intervening layer and the well layer,
The emission wavelength tends to shift to the shorter wavelength side. Conversely, if only the terminal well layer 11a is simply made thinner than the other well layers, the emission wavelength can be made longer. Therefore, in the light emitting layer having a quantum well structure, if the layer thickness 11a of the terminal well layer, which has a dominant influence on the emission wavelength, is made thinner than the other well layers, the crystallinity deteriorates. needless to dare constituting the well layer from Ga _1-X in _X N crystal layer indium composition ratio a convenience-obtained long wavelength is achieved in the emission wavelength.

When the thickness of the terminal well layer 11a is reduced, n
The degree of stress applied from the shaped barrier layer 10 and the intervening layer 12 increases. Therefore, the junction interface 15 with the terminal well layer 11a is formed.
The band bending in both the conduction band 16 at a and the valence band 20 at the interface 15b with the n-type barrier layer 10 is further increased. For this reason, the energy level formed in the low potential portions 18 and 21 due to the increase in the band bending becomes lower. Therefore, the transition energy between carriers is further reduced as compared with the case of a thick terminal well layer, resulting in a configuration convenient for obtaining long-wavelength light emission. In other words, unlike the conventional case, the gallium nitride-indium mixed crystal having a high indium composition ratio, which is inferior in crystallinity, does not need to constitute a terminal well layer, and a configuration that is more advantageous for obtaining long-wavelength emission can be obtained. There are advantages.

This longer wavelength phenomenon is a phenomenon completely opposite to the phenomenon developed from a conventional general quantum well structure having a rectangular potential configuration. In the conventional quantum well structure having a rectangular potential structure, the level formed in the well becomes higher as the thickness of the well layer, that is, the well width decreases. Therefore, the transition energy of electrons between quantum levels increases, and thus the emission wavelength becomes short. On the other hand, as described above, unlike this conventional quantum well structure, although a configuration that emits light of a long wavelength with a decrease in the well width is disclosed,
While the band structure sufficient to cause the wavelength extension phenomenon was completely unknown, the present invention clearly shows that it depends on the band structure based on the above-described bending of the conduction band and the valence band. is there.

According to the eighth embodiment of the present invention, a light emitting layer having a quantum well structure which provides light emission excellent in monochromaticity is provided. In particular, the terminal well layer is formed of indium as described in claim 7 of the present application. It is composed of a crystal layer having a multiphase structure with a restricted composition ratio. This is because a remarkable effect can be obtained in increasing the emission intensity. According to the configuration of the potential band of the present invention, it is necessary to use Ga _1-x In _x N having a high indium composition ratio, which deteriorates crystallinity, as a terminal well layer. Avoid irrationality. According to the present invention, the indium composition ratio (= X) is 0.1.
A gallium nitride-indium mixed crystal (G) having a relatively small indium composition ratio that does not cause deterioration in crystallinity of 3 or less.
a _{1 -X} In _x N: 0 ≦ X ≦ 0.3) can be easily used as a terminal well layer to provide a quantum well structure light emitting device that emits light of a long wavelength.

The terminal well layer composed of Ga _1-x In _x N (0 ≦ X ≦ 0.3) having an indium composition within the above-mentioned range and having a multiphase structure provides light emission with particularly excellent intensity. . The multi-phase structure means a plurality of domains or phases having different indium composition ratios (= X).
(e) is a crystal comprising the mixture of (e) (JP-A-10-562)
No. 02). If a phase (lump) predominantly present in the layer is the main phase, the multiphase structure is composed of the main phase and the phase (dependent phase) scattered subordinately within the main phase. The dependent phase is almost exclusively in the form of microcrystals, which are sometimes referred to as quantum dots.
t), a light emission excellent in intensity can be obtained. In addition, the main phase and the subordinate phase generally have different indium composition ratios, and therefore, the lattice strain generated at the junction interface between the main phase and the subordinate phase also contributes to the increase in emission intensity. Become.

For the terminal well layer having a multiphase structure, the same layer is made of, for example, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxial (MBE) method, or a halide or hydride (hydride). After the film is formed by the vapor phase epitaxy (VPE) method, the film can be formed constantly by heating and cooling under optimized conditions.

In the ninth embodiment of the present invention, a Ga _1-x In _x N (0 ≦ X ≦ 0.3) crystal layer having a multi-phase structure contains oxygen atoms at an appropriate concentration. Ga _1-X In
_The terminal well layer 11a is composed of an XN (0 ≦ X ≦ 0.3) crystal layer. By optimizing the oxygen concentration, the terminal well layer 101a that provides high-intensity light emission can be configured. In particular, Ga _1-x In _x N is preferably set to have an oxygen atom concentration of less than 5 × 10 ²⁰ cm ⁻³ , more preferably 1 × 10 ²⁰ cm ⁻³ or less.
(0 ≦ X ≦ 0.3) is suitable as a crystal layer for constituting the terminal well layer 11a. Oxygen atom concentration about 1 × 10 ¹⁵ c
If the terminal well layer is formed from a Ga _1-x In _x N (0 ≦ X ≦ 0.3) crystal layer having an extremely low oxygen atom concentration of not more than m ⁻³ or about 1 × 10 ¹⁴ cm ^−3, it will be rather high. In many cases, it does not always result in a strong luminescence. The range of oxygen atom concentration that is convenient for providing high intensity light emission is about 5 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ c
m ⁻³ or less.

Ga _{1 -X} with oxygen atom concentration in a suitable range
Means for obtaining an In _X N (0 ≦ X ≦ 0.3) crystal layer include, for example, a functional group containing oxygen or an impurity formed of an oxygen-containing substance when forming Ga _1-x In _x N by MOCVD. There is a method of using an organometallic compound containing a compound to which (function group) is added as a growth material. For example, trimethylgallium ((CH ₃ ) ₃ Ga:
TMG) was used as a Ga source, and trimethylindium ((CH
₃ ) Ga _1-x In _x N using ₃ In: TMI) as an In source
In the case of the film forming technique (0 ≦ X ≦ 0.3), TMG whose oxygen concentration is from several ppm by weight to tens of ppm by weight, and TMI whose oxygen concentration is from tens of ppm by weight to about 100 ppm by weight are used as a growth material. As a result, the precondition for keeping the oxygen atom concentration within the above-mentioned preferred range is set.

Ga _1-x In _x N (0 ≦
X ≦ 0.3) Another means for adjusting the oxygen atom concentration in the crystal layer is Ga _1-x In _x N (0 ≦ X ≦ 0.3).
Is formed in a growth atmosphere to which an oxygen-containing substance is intentionally added. Oxygen-containing substances include carbon monoxide (CO), carbon dioxide (CO ₂ ), and water (H ₂ O), but oxygen-containing substances such as nitric oxide (NO) and nitrogen dioxide (NO ₂ ) Since it contains nitrogen (N) which is a constituent element of a group III nitride semiconductor, it is preferably used from the viewpoint of suppressing the volatilization of nitrogen from a growth layer during film formation. For example, even if ammonia (NH ₃ ) gas containing water at a volume concentration of several to several tens ppm is used as a nitrogen source, Ga
The oxygen atom concentration in the _1-X In _X N crystal layer can be controlled.
The oxygen atom concentration in the Ga _1-x In _x N crystal layer can be quantified by instrumental analysis methods such as secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES).

[0057]

According to the band structure described in the first aspect of the present invention, an effect of selectively accumulating electrons in the region inside the terminal well layer is exhibited. Thereby, the electrons localized in the low potential portion are filled to a low potential level.

According to the arrangement of the terminal well layer according to the second aspect of the present invention, a low potential portion can be reliably created in the terminal well layer. In particular, as described in claim 3, the intervening layer and the n-type barrier layer joined to the terminal well layer are formed of a material having substantially the same composition and substantially the same layer thickness,
It exerts an action of applying a stress substantially evenly to the terminal well layer, and creates a state in which the presence or absence of the band bending at the junction interface of the terminal well layer and the degree of the bending can be easily controlled.

The invention according to claim 4 has an effect of selectively accumulating holes in a specific low potential region in the well layer. The low levels of electrons and holes at the low potential sites reduce the transition energies between carriers, thus resulting in longer wavelength emission than corresponds to the intrinsic bandgap.

Further, the invention according to claim 5 has an effect of reliably accumulating carriers in the well layer, and an effect of providing a band potential configuration which is advantageous in increasing the wavelength of light emission.

According to the sixth aspect of the present invention, the potential relationship between the first and second proximity well layers is such that electrons and electrons are preferentially contained in the first proximity well layer, that is, the terminal well layer. It acts to accumulate holes. This acts to make the emission from the quantum well structure monochromatic.

Further, the terminal well layer having a thickness smaller than that of the other well layers according to the invention of claim 7 has an effect of providing a potential configuration capable of easily achieving a longer emission wavelength.

The structure of the terminal well layer described in claim 8 has the function of increasing the intensity of light emitted from the terminal well layer. In particular, the terminal well layer in which the oxygen atom concentration is defined according to claim 9 has an action of further increasing the intensity of light emission.

[0064]

(Embodiment 1) In Embodiment 1, the present invention will be specifically described using a light emitting diode (LED) having an SQW structure as an example. FIG. 5 is a schematic diagram illustrating a cross-sectional structure of the LED 40 including the laminated structure 41 manufactured in the present example.

On the (0001) plane (c plane) of the crystal substrate 400 made of sapphire (α-Al ₂ O ₃ single crystal),
A buffer layer 401 made of undoped gallium nitride (GaN) composed mainly of single crystal at the junction interface with the substrate 400 and having an upper layer mainly composed of polycrystal or amorphous.
Deposited at 50 ° C. Buffer layer 40 having a thickness of about 17 nm
1, an undoped n-type GaN layer 4 having a carrier concentration of about 2 × 10 ¹⁷ cm ⁻³ and a layer thickness of about 0.5 μm.
02 is deposited. On the undoped n-type GaN layer 402, the n-type GaN layer 403 in which the doping concentration of silicon (Si) is increased in the direction of increasing the layer thickness, that is, the carrier concentration is gradually increased in the direction of increasing the layer thickness. Has been deposited.

Using this n-type GaN layer 403 as a lower n-type cladding layer, an undoped n-type GaN having a layer thickness of 20 nm (carrier concentration = 4 × 10
^A barrier layer 404 of ¹⁷ cm ^-3 ) was deposited.

On the barrier layer 404, a well layer serving as a terminal well layer 405 was deposited at 890 ° C. The terminal well layer 405 is
Undoped n-type Ga _0.88 In _0.12 N with a layer thickness of about 7 nm
It consisted of. Cyclopentadienyl indium (C ₅ H ₅ I
n) as an indium source (J. Crystal Gr)
owth, 107 (1991), pp. 360-364), the formation of the n-type Ga _0.88 In _{0. 12} N termination well layer 405, ends with stopping the supply to the atmospheric pressure MOCVD reactor of both raw materials I let it. After the formation of the terminal well layer 405, a growth interruption period in which the supply of the source gas to the MOCVD reactor is stopped is provided for 3 minutes, during which only the ammonia (NH ₃ ) gas is allowed to flow and the inside of the MOCVD reactor is The indium source and the gallium source were swept and eliminated such that there was no residue.

After the growth was interrupted, n-type GaN of the same material and having the same thickness as the n-type barrier layer 404 was deposited as the intervening layer 406. The carrier concentration of the intervening layer 406 is about 7 ×
It was 10 ¹⁶ cm ^-3 . That is, the n-type intermediate layer 406 is made of a material having the same conductivity type as the n-type barrier layer 404, but has a lower carrier concentration than the n-type barrier layer 404.
It was composed of a higher resistance and higher purity group III compound semiconductor crystal layer.

The above-described n-type barrier layer 404 and intervening layer 406
The light emitting part 42 having the SQW structure is sandwiched between the well layer 405 and
Was configured. The steepness at the junction interface 43 between the n-type intervening layer 406 and the well layer 405 is generally determined by the transition distance required for reducing the atomic concentration by two orders of magnitude from the average concentration in the well layer 405 and the indium (In) concentration. It was about 14 nm when measured by a simple SIMS analysis means. This steepness was sufficient to cause bending (bending) of the conduction band at the junction interface 43 between the n-type intervening layer 406 and the n-type well layer 405.

On the n-type intermediate layer 406, a magnesium (Mg) -doped p-type Al _0.15 Ga _0.85 N layer was deposited as a p-type cladding layer (layer thickness = 15 nm) 407. On the p-type cladding layer 407, a p-type Al _Y Ga _1-Y N (Y = 0.15 →) in which the aluminum (Al) composition ratio is decreased substantially linearly from 0.15 to 0 in the direction of increasing the layer thickness 0) layer as a contact layer (layer thickness = 0.1 μm, carrier concentration = 2 × 10 ¹⁷⁾
cm ⁻³ ) 408 to form a laminated structure 41.

The n-type cladding layer 40 exposed by performing plasma etching processing on the laminated structure 41 through patterning processing using a known photolithography technique
On the surface of 3, an n-type ohmic electrode 4
09 was provided. Further, a p-type ohmic electrode 410 was provided on the surface of the p-type contact layer 408 to constitute the LED 40.

Between the ohmic electrodes 409 and 410,
A DC voltage of 3.5 V (V) was applied, and a forward current of 20 mA (mA) was passed to cause the LED 40 to emit light. The center wavelength of the emission is about 450 nm, than corresponds to the Ga _{0. 88} In _0.12 N of bandgap at room temperature which constitutes a terminating well layer 405 (about 3.1 eV), about 0.3
Long wavelength light emission corresponding to a transition energy as low as about 4 eV was obtained. Further, the half width of the light emission was about 13 nm. In a chip state, the emission intensity measured using a general integrating sphere reached about 23 microwatts (μW). That is, in the present embodiment, the terminal well layer having a valence band structure bent to the low potential side is used as the light emitting layer.
An LED providing light emission excellent in both monochromaticity and intensity was obtained.

(Embodiment 2) In this embodiment, the present invention will be specifically described by taking as an example a case where an LED having a light emitting layer having a multiple quantum well structure (MQW) including the potential structure of the present invention is formed. Will be described. FIG. 6 shows L of the present embodiment.
It is a schematic diagram which shows the cross-section of ED50. Crystal substrate 40
The configuration from 0 to the n-type cladding layer 403 was as described in Example 1.

N-type Ga constituting n-type cladding layer 403
On the N layer, undoped n-type GaN is applied to the barrier layer 500.
A light-emitting layer 52 composed of a multi-quantum well structure 51b in which a pair of stacked structural units 51a are stacked in four cycles, using undoped n-type Ga _0.90 In _0.10 N as a well layer 501, is disposed. The thickness of the barrier layer 500 was about 15 nm. The thickness of the well layer 501 was 4 nm. Barrier layer 500
And the carrier concentration of the well layer 501 is 5 × 10 ¹⁷
cm ^-3 . In this MQW structure 51b, an undoped n-type Ga
N is a barrier layer 500, and the terminal well layer 501a is an n-type G layer.
a _0.90 In _0.10 N.

The well layers 501c, 501d and the barrier layer 5 on the n-type cladding layer 403 side after the second proximity well layer 501b adjacent to the terminal well layer (first proximity layer) 501a.
No measures have been taken to achieve the steepening of the junction interface with 00. That is, the other well layers 501c to 501d including the second adjacent well layer 501b are formed on the barrier layer 500 so as to be temporally continuous, and the growth interruption operation is not performed. On the other hand, when forming the terminal well layer 501a that terminates the light emitting layer 52 of the MQW structure 51b, after the film formation of the n-type barrier layer 500a at the final end is completed, the terminal well layer 501a is continuously connected temporally. 501a without forming a film,
The supply into the OCVD growth furnace was intentionally stopped for 4 minutes. Depending on the presence or absence of this growth interruption, the termination well layer 501
The degree of bending of the valence band at the interface with the n-type barrier layer 500a toward the lower potential side is larger than that of the other well layers 501c to 501d including the second adjacent well layer 501b. By the above-described growth interruption operation, the transition distance relating to the indium atom concentration described in Example 1 at the junction interface between the terminal well layer 501a and the n-type barrier layer 500a is set to about 12 n.
m.

On the terminal well layer 501a, an aluminum gallium nitride mixed crystal (Al _0.05 Ga _0.95 N) having a thickness of 20 nm, the same as that of the n-type barrier layer 500a at the final end, and an aluminum composition ratio of 0.05. N-type intermediate layer 50 made of
3 was deposited. The n-type intermediate layer 503 includes the n-type barrier layer 500.
Although it is composed of a material having substantially the same composition as that of the barrier layer 500a, the carrier concentration is lower than about 2 × 10 ¹⁶ cm ^−3, which is lower than that of the barrier layer 500a.

The n-type intervening layer 503 is formed on the terminal well layer 501a.
During the deposition, the growth interruption time was provided as described above. It is not necessary to make the growth interruption time uniform, but n
The growth interruption time before depositing the intervening layer 503 was also set to 4 minutes as in the above case. Thus, the terminal well layer 50
1a, it is necessary to reduce the indium atom concentration by two orders of magnitude from the junction interface with the n-type intermediate layer 503.
The distance (transition distance) to the inside of the intermediate layer 503 is about 13 n.
m.

On the n-type intermediate layer 503, the p-type cladding layer 407 and the p-type contact layer 408 described in the first embodiment are formed.
Were sequentially laminated to form a laminated structure 51.

The p produced by processing the laminated structure 51
About 3.4 to 3.5 for the LED 50 having the n-junction DH structure
When a forward voltage of V was applied and a forward current of 20 mA was passed, blue light emission having a center wavelength of light emission of about 470 nm was obtained. That is, G constituting the terminal well layer
About 3.1 which is a forbidden band of a _0.90 In _0.10 N.
Light emission corresponding to a transition energy of about 2.64 eV, which is about 0.46 eV lower than eV, was obtained. The half width of the emission spectrum was further narrowed to about 12 nm. The light emission intensity in a chip state was as high as about 25 μW.

(Embodiment 3) In the present embodiment, the present invention will be specifically described by taking as an example a case where an LED having the components described in claim 7 is manufactured.

In this embodiment, when the MQW structure having four periods described in the second embodiment is formed, the termination well layer 50 is formed.
The thickness of the n-type Ga _0.90 In _0.10 N crystal layer constituting the first near well layer 501 b and the subsequent well layers 50 b
It comprised so that it might be thinner than 1c-501d. That is,
The layer thickness of the terminal well layer 501a was 5 nm, and the layer thicknesses of the other well layers 501b, 501c to 501d were 10 nm. Thus, the second embodiment differs from the second embodiment in that the termination well layer 501 is provided.
An LED was constructed from a laminated structure obtained by changing only the layer thickness of a.

Approximately 3.2 between the n-type and p-type ohmic electrodes
A forward voltage of V was applied, and a forward current of about 20 mA was passed to emit light. The center wavelength of the light emission is the same as in Example 2.
The wavelength was about 490 nm, which was longer than that of the LED. This wavelength corresponds to Ga _0.90 In _0.10 constituting the well layer.
This corresponds to a transition energy of about 2.5 eV, which is smaller by about 0.57 eV than the normal band gap of N, which is about 3.1 eV. That is, even if the composition of the gallium-indium nitride mixed crystal constituting the terminal well layer is not changed, the emission from the light emitting layer having the multiple quantum well structure can be made to have a longer wavelength by simply reducing the layer thickness of the terminal well layer. Was shown. Further, the half width of the emission spectrum was about 14 nm, and the emission intensity in the chip state reached as high as about 27 μW after performing visibility correction. Than this,
According to the configuration described in the present example, it was shown that a quantum well structure light emitting device capable of emitting relatively long wavelength visible light, which is excellent in monochromaticity and strength, can be provided.

(Comparative Example 1) LE similar to that described in Example 3
In forming D, that is, in manufacturing an LED having an MQW structure 51b in which the thickness of the terminal well layer 501a is made thinner than the other well layers 501b to 501d,
The steepness at the junction interface between the second proximity well layer 501b and both the barrier layer 500a and the n-type barrier layer 500b on the n-type intervening layer 503 side is improved. That is, after the growth of the n-type barrier layer 500b is completed, a growth interruption time of one minute is provided, and after the growth of the second proximity well layer 501b,
By providing a 1 minute growth interruption time,
The steepness of both junction interfaces related to the adjacent well layer 501b was made substantially the same. Thus, the MQW structure 51b including the second proximity well layer 501b having a low potential portion in both the conduction band and the valence band as in the terminal well layer 501a.
Was formed.

The transition distance described in Comparative Example 1, which was obtained based on the analysis result by AES, was about 15 nm at both junction interfaces of the second terminal well layer 501b. Judging from this, the steepness was inferior to the transition distance of the terminal well layer 501a by about 3 to 4 nm.

In the same manner as described in Examples 1 to 3, pn junction type DH structure LEDs were manufactured and the light emission characteristics were evaluated. In comparison with the characteristics of the LED of Example 3, the center wavelength of light emission was slightly longer at about 505 nm due to the influence of the inflection of the band formed in the terminal well layer. On the other hand, as shown in the emission spectrum 53 in FIG. 7, the LED of this comparative example 1 has a secondary spectrum having a center wavelength of about 480 nm on the shorter wavelength side in addition to the main spectrum 53a giving the center emission wavelength. The generation of the spectrum 53b was observed. Due to the appearance of the secondary spectrum 53b, the half-value width was about 21 nm, which was inferior to that of the emission spectrum 53 from the LED 50 of Example 3.

As is clear from the comparison of the emission spectra of FIG. 7, the secondary spectrum 53b
It does not occur from D50. On the other hand, the second adjacent well layer 5
When 01b is formed of a well layer having a low potential portion at the junction interface with the barrier layers 500a and 500b, a secondary spectrum 53b that disturbs monochromaticity of light emission appears. Therefore, such a secondary spectrum 53b is interpreted as being derived from the second proximity layer 501b having the potential configuration as described above. In other words, in the light-emitting layer having a multiple quantum well structure (MQW), to improve the light-emitting characteristics such as making the emission wavelength uniform or narrowing the half-width of the emission spectrum, The result teaches that the potential drop of the conduction band and the valence band in the two adjacent well layers should be suppressed as much as possible.

(Embodiment 4) In this embodiment, in particular, a case where a quantum well structure LED having excellent light emission intensity and having a light emitting layer (terminal well layer) having the structure described in claim 8 and 9 is manufactured. The present invention will be specifically described by way of examples.

In constructing a laminated structure similar to that described in Example 1 for LED use (see FIG. 5), an n-type barrier layer 4 was used.
After the completion of the film formation of No. 04, the growth interruption operation described in Example 1 was performed before the film formation of the terminal well layer 405 was started.

In this embodiment, the terminal well layer 405 is composed of an n-type gallium-indium nitride mixed crystal (Ga _0.82 In _0.18 N) having a multiphase structure containing oxygen. Terminal well layer 4
05 is formed using the atmospheric pressure MOCVD technique,
Organic compounds having a methoxy (-OCH ₃ ) group added thereto are used as oxygen-containing impurities in an amount of about 60 ppm by weight.
Trimethylindium ((CH ₃ ) ₃ I)
n) was used as the In source. Thereby, the oxygen atom concentration is reduced to about 8
× 10 ¹⁸ cm ^-3 and an indium composition ratio of 0.18
Undoped n-type Ga _0.82 In _0.18 N was formed.

The layer thickness is about 5 nm, and the carrier concentration is about 5 nm.
After the film formation of the terminal well layer 405 of × 10 ¹⁷ cm ⁻³ is completed at 885 ° C., the temperature is increased at a rate of about 100 ° C./min to 1070 ° C., which is the growth temperature of the next n-type intermediate layer 406. The temperature rose in minutes. The time required for this temperature rise and the MOC of the source gas
A growth interruption time was provided for a total of 5 minutes in combination with the 3 minutes when the supply to the VD reactor was interrupted. By providing a period of growth interruption before and after the formation of the terminal well layer 405, the steepness at the junction interface between both the n-type barrier layer 404 and the n-type intervening layer 406 is set to about 14 nm.

Thereafter, the same p-type Al _0.15 Ga _0.85 N cladding layer 407 as in the first embodiment was formed at 1070 ° C. for 3 minutes.
Grew. p-type Al _0.15 Ga _0.85 N cladding layer 40
After 10 minutes, the aluminum composition ratio (=
X) p-type Al _x Ga ₁ -xN (X = 0.15 → 0) with a composition gradient that reduces X) from 0.15 toward 0 toward the surface
A contact layer 408 was grown. p-type contact layer 40
After the film formation of No. 8 was completed, the film was cooled to 950 ° C. at a rate of about 40 ° C./min. Continue from 950 ° C to 650 ° C at 15 ° C
Per minute. The terminal well layer 405 is subjected to such two-stage cooling with different cooling rates, and the terminal well layer 4
Sample No. 05 was a crystal layer having a multiphase structure having different indium composition ratios.

FIG. 8 is a transmission electron microscope (TEM) image showing the crystal structure inside the terminal well layer 405 after the cooling step. The terminal well layer 405 is
Ga _1-X I with an indium composition ratio (= X) of 2-3%
a main phase S composed of n _x N and an indium composition ratio of about 15
It has a multi-phase structure composed of a dependent phase T of microcrystal crystal of Ga _1-X In _X N to about 25%. Subject phase S
In many of the boundary regions between the indium phase and the dependent phase T, the existence of a region U containing lattice strain which is considered to occur due to a difference in lattice constant caused by a difference in indium composition ratio between the two was recognized. The oxygen atom concentration in the terminal well layer 405 is
Since the detection sensitivity was inferior to heavy metals, accurate quantification was not achieved. However, oxygen is contained in both the phase region of the main phase S and the phase region of the dependent phase T.
It appeared to be more present inside the dependent phase T.

In the same manner as described in Example 1, a quantum well structure LED was manufactured. From the LED, the emission wavelength is about 45
Emission of a blue-green band of 0 nm was emitted. This is about 0.34 eV compared to about 3.0 eV which is the original band gap of Ga _0.82 In _0.18 N constituting the terminal well layer.
Light emission corresponding to a low transition energy was obtained. The half width of the emission spectrum was about 12 nm. While these characteristics did not differ from those of the LED of Example 1, the emission intensity was higher than that of the LED of Example 1.
Of about 30 μW, which is about 30% higher than the intensity of Thus, the terminal well layer composed of Ga _1-X In _X N having a multiphase structure containing an appropriate amount of oxygen in addition to an indium composition ratio capable of maintaining a high crystallinity of 0.3 or less,
In particular, to provide a quantum well structure light emitting device with high emission intensity,
It was shown to be effective.

[0094]

According to the first aspect of the present invention, an indium-containing group III material having a high indium composition ratio and inferior crystallinity is exhibited while exhibiting the original characteristics of a quantum well structure providing light emission with excellent monochromaticity. Even if the nitride semiconductor layer is not intentionally used as a light emitting layer, a band which is convenient for promoting a longer wavelength of light emission at the junction surface of the terminal well layer and the n-type intervening layer is generated to a low potential side. Thus, there is an effect that a quantum well structure light emitting element convenient for increasing the wavelength of light emission can be provided.

According to the second and third aspects of the present invention, in addition to the first aspect of the present invention, the terminal well layer is formed of an n-type barrier layer and an n-type barrier layer.
Since it is sandwiched between the intervening layers and has a configuration that is convenient for generating band bending in the terminal well layer, there is an effect that a quantum well structure light-emitting element that is convenient for increasing the wavelength of light emission can be provided.

According to the fourth aspect of the invention, since holes are effectively accumulated in the low potential portion of the valence band, a transition energy smaller than the normal band gap is given,
There is an effect that it is possible to provide a quantum structure light emitting device having a configuration particularly convenient for increasing the wavelength of light emission.

According to the fifth aspect of the present invention, the degree of bending of both the conduction band and the valence band, which works well to shift the emission wavelength to the longer wavelength side while securing steepness at the junction interface. Is increased, the transition energy of carriers is further reduced, and there is an effect that a quantum well light emitting device which is convenient for providing long-wavelength light emission can be provided. In particular, according to the seventh aspect of the present invention, since the terminal well layer is formed from a thinner layer capable of more clearly exhibiting a longer wavelength of light emission due to band bending due to the steepness of the junction interface, the light emission is improved. Provided is a quantum well light emitting device that can easily achieve a longer wavelength.

According to the invention of claim 6, in the multiple quantum structure, the degree of bending of both the conduction band and the valence band in the terminal well layer is compared with that of the other well layers. In general, since the expansion of the non-uniformity of the transition energy between carriers is suppressed, a quantum well structure light emitting element which is excellent in monochromaticity and emits light of a long wavelength can be provided.

According to the eighth aspect of the present invention, the terminal well layer of the quantum well structure is not a single composition but has a multiphase structure having a different indium composition, and the indium composition ratio which does not remarkably cause the deterioration of crystallinity is improved. Since it is composed of gallium / indium nitride having a low indium composition ratio of 0.3 or less, high-intensity light emission is provided, and therefore, there is an effect that a high-intensity quantum well structure light-emitting device can be provided.

Further, according to the ninth aspect of the present invention, as described in the eighth aspect of the present invention, a low indium composition ratio and
In forming the terminal well layer from a gallium nitride-indium mixed crystal having a multi-phase structure, a quantum well structure light emitting device having a further excellent light emission intensity, particularly because the concentration of oxygen atoms contained in the well layer is adjusted to an appropriate amount. There is an effect that can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy band structure of a pn junction type DH structure light emitting unit having a light emitting layer of a single quantum well (SQW) structure.

FIG. 2 is a diagram illustrating an energy band structure of a pn junction type DH structure light emitting unit including a light emitting layer having a multiple quantum well (MQW) structure.

FIG. 3 is a diagram showing a potential configuration in an SQW structure according to the present invention.

FIG. 4 is a diagram showing a potential configuration in an MQW structure according to the present invention.

FIG. 5 is a schematic sectional view of the LED of Example 1.

FIG. 6 is a schematic sectional view of an LED according to a second embodiment.

FIG. 7 is an emission spectrum of the LED described in Example 3 and Comparative Example 1.

FIG. 8 is a schematic TEM image showing a crystal structure inside a terminal well layer described in Example 4.

FIG. 9 is a diagram showing a basic energy band structure of a conventional single quantum well (SQW) structure.

FIG. 10 is a diagram showing a rectangular potential configuration of an energy band structure of an SQW structure.

[Explanation of symbols]

010,011,10,404,500,500a, 5
00b: barrier layers 012, 11, 11a, 11b, 11c, 11d, 11
e, 501a, 501b, 501c, 501d: Well layer 013, 24: Original bandgap of the material constituting the well layer 014, 015: Bandgap of barrier layer 016: Potential well 017, 16: Conduction band 018 , 20: valence band 019, 020: quantum level formed on the conduction band side 021, 022: quantum level formed on the valence band side 023, 024, 23: transition energy 1: light emitting portion 1a: light emission Layer 1b: Single quantum well 1d: Multiple quantum well 11a, 405, 501a: Terminal well layer 11b, 501b: Second proximity well layer 12, 406, 503: Intermediate layer 13, 403: N-type cladding layer 14, 407: p-type cladding layers 15a, 43: junction interface between terminal well layer and intervening layer 15b: junction interface between terminal well layer and barrier layer 15c: second adjacent well layer and barrier layer Junction interface on the side of the intervening layer 15d: Junction interface between the second proximity well layer and the barrier layer 16a: Conduction band level (Eco) 16b: Bend end of the conduction band (Ec) 16c: Potential difference in the conduction band 17: Fermi level 18 : Low potential portion on the conduction band side 19: electron 20 a: valence band level (Evo) 20 b: bent end of the valence band (Ev) 20 c: potential difference of the valence band 21: low potential portion on the valence band side 22 : Hole 25a: Degree of bending on the conduction band side in the terminal well layer 25b: Degree of bending on the valence band side in the terminal well layer 25c: Degree of bending on the conduction band side in the second adjacent well layer 25d: Degree of bending on the valence band side in the second proximity well layer 40, 50: LED 41, 51: stacked structure 400: crystal substrate 401: buffer layer 402: n-type GaN layer 408: contact layer 409: -Type ohmic electrode 410: p-type ohmic electrode 51a: quantum well constituent unit 51b: multiple quantum well structure 52: light emitting layer 53, 54: emission spectrum 53a: main emission spectrum 53b: secondary emission spectrum S: main phase T: Dependent phase U: Strain-containing region

Claims (9)

[Claims] A pn junction double hetero (DH) formed on one surface of a crystal substrate and having an n-type light emitting layer sandwiched between n-type and p-type cladding layers made of a group III nitride semiconductor crystal layer. In the light emitting device having the structure, the n-type light emitting layer has a single or multiple quantum well structure, and a well layer (terminating well layer) which constitutes an end of the quantum well structure.
An intermediate layer made of an n-type group III nitride semiconductor is disposed between the p-type clad layer and the p-type clad layer, and the terminal well layer is located in a region near a junction interface between the n-type intermediate layer and the terminal well layer. Indium (In) -containing n-type group III nitride semiconductor crystal having a potential configuration in which a conduction band of the terminal well layer is bent downward and convex toward a lower potential side toward a Fermi level. A quantum well structure light emitting device comprising a layer. 2. The terminal well layer, wherein the n-type intervening layer comprises:
2. The quantum well structure light emitting device according to claim 1, wherein the n-type intervening layer is interposed between the n-type barrier layer and an opposing n-type barrier layer with a terminal well layer interposed therebetween. 3. The quantum well structure light emitting device according to claim 2, wherein the n-type barrier layer has substantially the same composition and substantially the same thickness as the n-type intervening layer. 4. The terminal well layer has a low potential region in a region near a junction interface with the n-type barrier layer, in which a valence band of the terminal well layer is bent upward and convex toward Fermi level. 4. The device according to claim 2, wherein
3. The quantum well structure light emitting device according to item 1. 5. The terminal well layer has an energy difference (ΔE) between an original potential level (Eco) of a conduction band and a low potential end (Ec) dropped to the Fermi level side.
c = | Eco−Ec |) and the energy difference (ΔEv =) between the original potential level (Evo) of the valence band and the low potential end (Ev) that has dropped to the Fermi level side.
| Evo−Ev |) and the total energy difference (ΔEc +
The quantum well structure light emitting device according to claim 4, wherein the quantum well structure has a conduction band and a valence band that make ΔEv) 0.4 electron volts (eV) or more. 6. The n-type light-emitting layer has a multiple quantum well structure, and the layer thickness of the terminal well layer is such that the total energy difference (ΔEc + ΔEv) is larger than the total energy difference of other well layers. The quantum well structure light emitting device according to claim 4, wherein the light emitting device has a large diameter. 7. The n-type light emitting layer has a multiple quantum well structure, and the thickness of the terminal well layer is less than the thickness of another well layer. The quantum well structure light emitting device according to any one of the above. 8. The terminal well layer includes a main phase having an indium composition ratio (= X) of 0.3 or less and a strained layer having a different indium composition ratio from the main phase and having a junction boundary region with the main phase. N _-type gallium indium nitride (Ga _1-x In _x N: 0 ≦ X ≦ 0.
8. A light emitting device having a quantum well structure according to claim 1, wherein the light emitting device comprises: 9. The method according to claim 1, wherein the terminal well layer having the multiphase structure has an oxygen atom concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ²⁰ cm ^−3.
N _-type Ga _1-x In _x N (0 ≦ X ≦ 0.
3) The quantum well structure light emitting device according to claim 8, comprising a crystal.