JPH11186603A - Nitride semiconductor light emitting device - Google Patents

Abstract

(57) [Problem] To clarify the constituent requirements necessary for a dependent phase to efficiently act as a quantum dot, and to stably and excellently emit light from a light-emitting layer. SOLUTION: The present invention provides a nitride semiconductor light emitting device in which a light emitting layer 2 is an indium-containing group III nitride semiconductor layer having a multiphase structure composed of a main phase 21 and a dependent phase 22 having different indium compositions. It is characterized in that the dependent phase 22 is mainly composed of a crystal having a strained layer 23 at the boundary with the surrounding main phase 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device having a multiphase indium-containing group III nitride semiconductor layer composed of a main phase and a sub phase having different indium compositions as a light emitting layer.

[0002]

BACKGROUND general formula _{Al x Ga y In z N a} M 1-a (x + y
+ Z = 1, 0 ≦ x, y <1, 0 <z ≦ 1, 0 <a ≦ 1,
Indium (In) -containing group III nitride semiconductors represented by M (Group V element other than nitrogen) are used as light emitting layers of nitride semiconductor light emitting devices that emit short-wavelength light. In particular, gallium nitride-indium mixed crystal (Ga _b In
_1-b N: 0 ≦ b <1) is a typical constituent material of the light emitting layer (see Japanese Patent Publication No. 55-3834).
In one conventional example, the In composition ratio is 0.20 (20%).
Gallium nitride-indium mixed crystal (Ga _0.80 In
_0.20 N) is used as a light emitting layer of a blue light emitting diode (LED) having an emission wavelength of about 450 nanometers (nm). A gallium-indium nitride mixed crystal having an In composition ratio of 0.45 is used as a light emitting layer of a green LED having an emission wavelength of about 525 nm.

A gallium-indium nitride mixed crystal is also used as a well layer having a single or multiple quantum well structure forming a light emitting portion (see Japanese Patent Application Laid-Open No. 9-36430). Gallium nitride which has been widely used as a light emitting layer
It has been considered that the indium mixed crystal preferably has a homogeneous structure with a uniform In composition (see Japanese Patent Application Laid-Open No. 9-36430). However, it has recently been found that a gallium-indium nitride layer having a non-uniform In composition can be conveniently used as a light-emitting layer (Japanese Patent Application No. Hei 8-26).
No. 1044). This is a so-called gallium-indium nitride layer having a multi-phase structure composed of an aggregate of phases having different In composition ratios.

[0004] High output light emission from a multi-phase gallium indium nitride layer having a non-uniform In composition and "fluctuations" in the In composition as described above is attributed to quantum dots (dots) and the like. It is attributed to the quantized light emitter. A gallium-indium nitride layer having a multiphase structure is generally composed of a main phase (mother phase) occupying a large volume and a subordinate phase (see Japanese Patent Application No. 8-208486). The dependent phase usually has a different In composition ratio from the main phase. It is only in the case that the In composition ratio differs between the dependent phases. The subordinate phase generally forms a substantially spherical or island-like microcrystalline body and is scattered in the main phase.

[0005] In the prior art, it has been pointed out that the quantization level formed at the boundary between the microcrystalline body (dependent phase) and the main phase surrounding it is involved in the emission (Japanese Patent Application No. Hei 8-8). 2
No.61044). In general, the size of the microcrystal is several to several tens of nm in diameter and has a size sufficient to act as a quantum dot. The dependent phase as the quantum dot is an In-containing group III nitride semiconductor. It is considered to be involved in light emission from the light emitting layer composed of

[0006]

However, if good, I
Even if a subordinate phase (quantum dot) is involved in light emission from a light emitting layer made of an n-containing group III nitride semiconductor, light emission typified by light emission intensity and light emission wavelength resulting from light emission emitted from the light emitting layer At present, the technology for obtaining the characteristics stably is unknown, and the obtained light-emitting characteristics are unstable.

[0007] In the prior art, the main reason that the resulting emission characteristics are unstable is that the requirements necessary for the dependent phase to act as a quantized illuminant are not sufficiently defined. In order to stably obtain light emission characteristics, particularly high light emission intensity, it is necessary to clarify the constituent requirements for causing the dependent microcrystals to efficiently act as quantum dots.

[0008] The present invention has been proposed in view of the above,
Provided is a nitride semiconductor light-emitting device capable of stably and excellently emitting light obtained from a light-emitting layer by clarifying constituent components necessary for causing a dependent phase to efficiently act as quantum dots. With the goal.

[0009]

In order to achieve the above object, the present invention encloses the subphase and its surroundings so that the microcrystal constituting the subphase acts as a quantized luminescent medium. This defines the configuration of the region near the boundary with the main phase. That is, in the present invention, in the nitride semiconductor light-emitting device having a multi-phase structure indium-containing group III nitride semiconductor layer composed of a main phase and a sub phase having different indium compositions as the light emitting layer, the sub phase, It is mainly composed of a crystal having a strained layer at the boundary with the surrounding main phase.

[0010]

Embodiments of the present invention will be described below in detail. In the following description, a crystal phase that occupies a certain region spatially with a substantially constant In composition ratio (concentration) is simply expressed as a phase. A phase that occupies a large area spatially is called a main phase, and is scattered almost uniformly in the main phase or unevenly distributed in a region near a junction interface with another layer. The smaller phase is called the dependent phase. The main phase and the dependent phase are not distinguished by the magnitude of the In composition ratio but by the magnitude of the volume occupied spatially.

In most cases, the main phase is composed of a layered single crystal in which a single crystal layer is accumulated, but it may partially include a polycrystalline region or an amorphous substance. The main phase occupies a large area irrespective of the crystal form. In most cases, the dependent phase is in the form of fine crystals (microcrystals). The microcrystal is a single crystal, polycrystal, amorphous or a mixture of these crystal grains. Generally, the outer shape of the microcrystal is a substantially spherical or polygonal island. The size of the dependent phase is approximately the diameter or the width in the case of an island,
It is several to several tens of nm. A relatively large In precipitate having a size of several to several tens of μm may be generated using indium accumulated at a bonding interface with another layer as a nucleus.
A crystal having a size of about m is treated as a dependent phase.

In the present invention, the light-emitting layer is composed of an In-containing group III nitride semiconductor having a multiphase structure composed of a main phase and a subordinate phase. The average layer thickness of the layered body constituting the main phase is the layer thickness of the light emitting layer. Ultra-thin layers less than about 1 nm lack film continuity. The light-emitting layer formed of a discontinuous film causes inconvenience such as a problem in reducing the forward voltage of the light-emitting element. Conversely, if the thickness exceeds about 300 nm, the surface state is impaired, so that it cannot be conveniently used as a light emitting layer that contributes to an increase in light emission intensity. Therefore, the thickness of the light emitting layer is generally about 1
Desirably, the range is from about 300 nm to about 300 nm.

The light emitting layer can be composed of an In-containing group III nitride semiconductor to which impurities are intentionally added (doped). Undoped In-containing II without intentional addition of impurities II
It can also be composed of a Group I nitride semiconductor. In addition, the undoped layer and the impurity-doped layer may be formed in a multilayer structure. From the viewpoint of emission intensity, the layer thickness of the impurity-doped emission layer is
It is desirable to have a certain thickness. About 10nm to about 30
0 nm is preferred. In the case of an undoped light emitting layer, it is desirable to make it thinner. A preferred range is about 10 nm or less and about 1 nm or more.

In particular, the electric conduction type of the light emitting layer is n-type.
preferable. The carrier between the main phase and the dependent phase,
Is considered to be mainly responsible for the magnitude of the emission intensity
Because. Therefore, the light emitting layer transfers electrons to the majority (m
ajority) to be a carrier, that is, to be n-type
Is most preferred. The carrier concentration of the light emitting layer is approximately 10 ¹⁶
cm^-3About 1 × 10¹⁹cm^-3It is convenient to
It is. Make the carrier concentration of the main phase and that of the sub phase substantially the same.
You don't have to. For example, the main phase
Rear concentration is about 10¹⁸cm^-3Degree, that of the dependent phase is about 1
0¹⁷cm^-3In some cases, it may occur. Subject and subordinate
The degree of difference in carrier concentration from the genus
It is preferable to set the above range as a whole.

The dependent phase is generated from inside the main phase.
is there. For example, there is a potential strain region or
Contained in the main phase, agglomerated in the dense area of crystal defects
In is generated with In as a nucleus. The density of the dependent phase in the main phase is
When extremely large, light emission from the main phase (light-emitting layer) is monochromatic
It lacks sex. Dependent phase density 2 × 10¹⁸cm ^-3
When the value exceeds, the monochromaticity of light emission deteriorates rapidly. Therefore,
Genus phase density 2 × 10 ¹⁸cm^-3Preferably
No. Particularly, an undoped light emitting layer having a layer thickness of 20 nm or less.
The density of the dependent phase is 5.0 × 10^{twenty three}× t (here
And t: layer thickness (cm) or less. Obedience
If the density of the genus phase is within the above range, the half width is 15 nm or less.
Light emission with excellent monochromaticity can be obtained as described below.

In general, In is vapor-phase grown by MOCVD or the like in a temperature range of 650 ° C. or more and less than 950 ° C.
In some cases, the light emitting layer made of the contained group III nitride semiconductor is separated into multiple phases in an as-grown state during growth. However, in a multiphase structure in an as-grown state, the size of the dependent phase is extremely uneven. as-
When a heat treatment is performed on the grown In-containing group III nitride semiconductor layer, a subordinate phase can be generated stably with the main phase as a parent, and a multiphase structure can be formed. In a heat treatment method for stably forming an In-containing group III nitride semiconductor layer having a multiphase structure serving as a light emitting layer, (a) a temperature rising rate from a growth temperature of the light emitting layer to a heat treatment temperature; In addition to the holding time at the heat treatment temperature, the size of the dependent phase can be made uniform by optimizing the cooling rate particularly when the temperature is lowered from the heat treatment temperature. The uniformity of the size of the dependent phase depends on the I in the dependent phase.
This is particularly effective in improving the uniformity of the emission wavelength and the monochromaticity of the emission as well as the uniformization of the n concentration (composition ratio).

In the present invention, the structure of the boundary region between the main phase and the subordinate phase in the light emitting layer is specified. That is, the dependent phase of the present invention is characterized by having a strained region (strained layer) at the boundary with the main phase surrounding it. Then, the number of the dependent phases accompanying the strained layer is set to account for 50% or more of the total number of the dependent phases.

The dependent phase whose outer periphery is surrounded by the strained layer appropriately adjusts the cooling rate particularly from the heat treatment temperature in the heat treatment of the light emitting layer for stably forming the above-mentioned multiphase structure. It can be formed by things. It is the most preferred cooling method to change the temperature from the heat treatment temperature at which the temperature is preferably 950 ° C. or more and 1200 ° C. or less as a desirable treatment temperature while changing the speed. In particular, 950 ° C from the heat treatment temperature
To 650 ° C / min.
The cooling method including a step of lowering the temperature to 20 ° C. per minute at a rate of 20 ° C. or less is a method capable of stably forming a dependent phase having a strained layer on the outer periphery. 20 from heat treatment temperature to 950 ° C
If the temperature is decreased at a rate of not more than ° C./min, the surface state of the light emitting layer cannot be maintained in the first place, resulting in a light emitting layer lacking in flatness. Rapid cooling from 950 ° C. to 650 ° C. above 20 ° C. per minute is disadvantageous as it leaves more than an appropriate amount of strained layer around the dependent phase.

It is not necessary to separately and specially perform the above-mentioned heat treatment for forming a multi-phase structure. For example, the heat treatment can be replaced by a growth operation for growing, for example, a gallium nitride-based layer or an aluminum-gallium nitride-based mixed crystal layer on the light-emitting layer formed of an In-containing group III nitride semiconductor layer. This is because the growth temperature at the time of growing these layers on the light emitting layer is in the preferable heating temperature range described above.

Whether or not the In-containing group III nitride semiconductor layer has a multiphase structure can be confirmed by a normal cross-sectional TEM technique using a transmission electron microscope (TEM).
In the bright-field cross-sectional TEM image of the gallium-indium nitride mixed crystal having a multiphase structure, the dependent phase is imaged with a black contrast such as a substantially circular trapezoidal or polygonal cross section. The black contrast may be caused by crystal defects such as dislocations. The contrast due to dislocations and the like is generally linear. Whether or not the phase is dependent on the shape of the contrast,
Also, the shape of the dependent phase can be known. The density of the dependent phase in the main phase can be measured from the density of the contrast caused by the dependent phase. According to a so-called analytical electron microscope having a composition analysis function such as an electron probe microanalyzer (EPMA), each of the main phase and the dependent phase has In.
The composition ratio can be analyzed. The difference in the In composition between the main phase and the subordinate phase (“fluctuation”) is expressed by X which is simply called a four-crystal method.
It can also be analyzed from the line precision diffraction method.

The presence or absence of the strain layer around the dependent phase can be observed from a high-magnification cross-sectional TEM image. A high magnification of several million times is suitable for observation. FIG. 1 is an example of a crystal lattice image when the light emitting layer according to the nitride semiconductor light emitting device of the present invention is imaged by a transmission electron microscope (TEM). This crystal lattice image was taken by a 2 million times bright field cross-sectional TEM technique. Hereinafter, description will be made with reference to FIG.

In the figure, the light emitting layer 2 is made of indium (I
n) It has a multiphase structure composed of a main phase 21 and a sub phase 22 having different compositions, and a strain is present around the sub phase 22 existing in the main phase 21 which is a base of the light emitting layer 2. Layer 23
Is attached. That is, the dependent phase 22 is composed of the surrounding main phase 2
The crystal body has a strained layer 23 at the boundary with the main body 1 and is formed around the center of the main body (hereinafter referred to as “dependent phase main body”) 22a and the outer periphery of the dependent phase main body 22a. And a strain layer 23. Layer thickness d of strained layer 23
Is not always maintained substantially uniformly around the periphery, and may be distorted with respect to the dependent phase main body portion 22a, for example, may be developed thick only in one direction.

Comparison of the distance between the crystal lattice planes shows that the main phase 2
1. It is recognized that the lattice intervals are different from each other inside the dependent phase main body portion 22a and the strained layer 23. That is, the strained layer 23
Is a region having a lattice plane (lattice image) interval and a lattice arrangement direction different from those of the main phase 21 and the subordinate phase main portion 22a on the lattice image. The interval between the lattice images of the strained layer 23 is intermediate between the main phase 21 and the dependent phase main portion 22a, and the arrangement of the lattice (image) may be messy.

The thickness d of the strained layer 23 surrounding the dependent phase 22
Affects the intensity of light emitted from the light emitting layer 2 having a multiphase structure. If the strained layer 23 is extremely thick, the effect of improving the light emission intensity will not be obtained. In order to obtain high-intensity light emission, the strained layer 23 has an appropriate thickness d. When the layer thickness (region width) d of the strained layer 23 is obtained, the thickness d of the strained layer 23 suitable for high-intensity light emission is 0.5 × D or less with respect to the size D of the dependent phase main body portion 22a. . When the dependent phase 22 is substantially spherical, the size D can be represented by a diameter. In the island-shaped dependent phase 22, the size D can be represented by the width.
For example, the thickness of the strained layer 23 is set to 10 (= 0.5 × 20) nm or less for a spherical dependent phase having a diameter of 20 nm.

As described above, the thickness d of the strained layer 23 is not necessarily substantially uniform, but the average thickness d of the strained layer 23 is 0.5
If it is less than × D, the effect will not be impaired. Strain layer 2
Even when 3 is extremely thin, it is not possible to achieve the effect corresponding to the improvement of the emission intensity. If a certain amount of the strain layer 23 does not exist between the main phase 21 and the dependent phase main body portion 22a, a band configuration for generating quantized carriers resulting in high-intensity light emission cannot be sufficiently created. It is thought that it is. At least about 5 mm as the thickness d of the strained layer 23
The degree is necessary, and is preferably 10 ° (= 1 nm) or more.

On the other hand, the maximum value of the thickness d of the strained layer 23 is 10 n
m or less. This is the preferred thickness of the strained layer in view of the fact that the In content of the In-containing group III nitride semiconductor layer, which is extremely generally used as the light emitting layer 2, is about 0.05 to about 0.5. . Therefore, the thickness d of the strained layer 23
Is preferably in the range of about 10 ° to 10 nm.

As described above, the thickness d of the strained layer 23 is determined by heating the light emitting layer 2 for forming a multiphase structure after the growth of the In-containing group III nitride semiconductor layer serving as the light emitting layer 2 is completed. It can be controlled by adjusting the cooling rate in the cooling step accompanying the treatment. In particular, the cooling (cooling) rate in the temperature range of 950 ° C. to 650 ° C. is a dominant factor that determines the thickness d of the strained layer 23. As described above, the cooling rate in the same temperature range is desirably 20 ° C. or less per minute. However, in order to set the thickness d of the strained layer 23 in the range of 10 ° to 10 nm, the cooling rate is 5 ° C. / Min to 20 ° C / min, good results can be obtained, and a more preferable cooling rate is 7 ° C / min.
Min to 15 ° C / min. When the temperature is lowered at a rate exceeding 20 ° C./min, the thickness d of the strained layer 23 increases and stably becomes 0.5 ×
It is difficult to reduce the value to D or less. Conversely, the cooling rate is 3 ° C per minute
If the thickness is less than the above, the thickness d of the strained layer 23 decreases, and it becomes impossible to secure even the minimum thickness of the strained layer of about 5 °.

As for the cooling rate in the cooling step, various cooling patterns can be adopted. For example,
From 950 ° C. to 650 ° C., cooling may be performed uniformly at a constant cooling rate, or cooling may be performed at various cooling rates. To give a specific example, 950
The temperature may be lowered at a rate of 15 ° C./minute from 800 ° C. to 800 ° C., and subsequently at a rate of 10 ° C./minute from 800 ° C. to 600 ° C. Also, start cooling at a constant rate from 950 ° C,
After holding at a certain temperature between 950 ° C. and 650 ° C. for a predetermined standby time, cooling to 650 ° C. may be started again. As described above, the advantage of maintaining the temperature at a substantially constant temperature for a predetermined standby time during the temperature lowering process is that the thickness d of the strained layer 23 around the dependent phase 22 can be made uniform. Therefore, the combined use of the temperature lowering rate and the temperature lowering treatment method of providing a waiting time according to the present invention can control the thickness d of the strained layer 23 and achieve the uniformity of the thickness d of the strained layer 23. There is. The presence of the strained layer 23 having a controlled and uniform thickness contributes to the improvement of the emission intensity and the monochromaticity of the emission through the uniformization of the quantum levels.

As described above, in this embodiment, the main phase 21 and the dependent phase 22 having different indium compositions from each other.
In the light-emitting layer 2 formed of an indium-containing group-III nitride semiconductor having a multiphase structure consisting of the following, the dependent phase 22 is mainly composed of a crystal having a strained layer 23 at the boundary with the surrounding main phase 21. As a result, the strained layer 23 present around the dependent phase 22 stably generates carriers contributing to an increase in emission intensity, and therefore, the crystals constituting the dependent phase 22 are quantized. Can be effectively used as a light emitting medium, and short-wavelength visible light output from the nitride semiconductor light emitting device including the light emitting layer 2 can be stably provided with high light emission intensity and excellent monochromaticity. can do.

Next, the nitride semiconductor light emitting device of the present invention will be described with more specific examples.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) The present invention relates to a light emitting diode (L).
ED) will be described. Each constituent layer constituting the laminated structure for LED use was sequentially formed on the substrate by the following procedure using a general normal pressure (atmospheric pressure) type MOCVD growth furnace.

FIG. 2 is a view showing a laminated structure according to the first embodiment of the present invention. In the figure, a laminated structure 11 is formed by being laminated on a substrate 100. The substrate 100 has a diameter of 2 inches (50 mm in diameter) and a thickness of about 90 μm.
(0001) (c-plane) -sapphire (α
-Al ₂ O ₃ single crystal) was used. On the substrate 100, trimethylgallium ((CH ₃ ) ₃ Ga), trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia (NH ₃ ) are used as raw materials by a normal atmospheric pressure MOCVD method to form aluminum gallium nitride (Al _0.8 A low-temperature buffer layer 100a made of Ga _0.2 N) was formed. The film formation was performed at 430 ° C. for exactly 3 minutes in a hydrogen stream. The flow rate of hydrogen is 8 liters per minute, and the flow rate of ammonia gas is 1 liter per minute.
Liters. The thickness of the low-temperature buffer layer 100a is 15 nm.
Met.

Next, on the low-temperature buffer layer 100a, a volume concentration
About 3 ppm of disilane (Si _TwoH₆) Containing hydrogen gas
Is added to the MOCVD reaction system and hydrogen-argon (A
r) n-type gallium nitride (GaN) in air stream at 1100 ° C
Layer 101 was deposited for 90 minutes. Disilane-hydrogen mixture
The addition amount of the combined gas into the system should be 10 cc / min.
It was precisely controlled by an electronic mass flow meter (MFC). This silicon
Carrying of n-type gallium nitride layer 101 doped with silicon (Si)
A concentration is about 3 × 10¹⁸cm^-3And the layer thickness is about 3 μm.
Was.

The temperature of the substrate 100 is increased from 1100 ° C. to 800
After the temperature is lowered to about 0 ° C., a light emitting layer 102 made of gallium indium nitride (Ga _0.82 In _0.18 N) having an average composition ratio of indium (In) of 0.18 is deposited on the n-type gallium nitride layer 101. did. The growth of the light emitting layer 102 was performed in an argon stream. The layer thickness of the light emitting layer 102 was 5 nm. Trimethyl gallium was used as the gallium source, and trimethyl indium was used as the indium source. Trimethylgallium is kept at a constant temperature of 0 ° C., and the flow rate of hydrogen for bubbling (bubbling) it is 1 c / min.
c was precisely controlled. Trimethylindium was kept at a constant temperature of 50 ° C. The flow rate of hydrogen gas accompanying the sublimated trimethylindium vapor is 13 c / min by MFC.
c. The flow rate of ammonia gas as a nitrogen source was set so that the V / III ratio during growth of the light emitting layer 102 was about 3 × 10 ⁴ . Here, the V / III ratio indicates the ratio of the concentration of the nitrogen source to the total concentration of the gallium source and the indium source supplied to the growth reaction system. The growth rate of the light emitting layer 102 was lower than that of the n-type gallium nitride layer 101 to about 2 nm / min.

After the growth of the light-emitting layer 102, the temperature of the substrate 100 was rapidly increased from 800 ° C. to 100 ° C./minute to 1100 ° C. for 3 minutes in an argon stream. While waiting at the same temperature for 1 minute, the composition of the atmosphere of the MOCVD reaction system was changed to a mixed gas of argon and hydrogen, and a magnesium (Mg) -doped aluminum-gallium nitride mixed crystal layer (Al _0.15 Ga _0.85 N) layer was used. 103 is the light emitting layer 102
Deposited on top. The growth rate is about 1.
It was set to about 3 nm / min, which was equivalent to 5 times. The growth was continued for 10 minutes to obtain a mixed crystal layer having a thickness of about 30 nm. The doping source magnesium using bis cyclopentadienyl magnesium _{(bis- (C 5 H 5)} 2 Mg). The supply amount of the magnesium doping source to the MOCVD reaction system was set at 8 × 10 ^-6 mol / min. The concentration of magnesium atoms in the Mg-doped aluminum-gallium nitride layer 103 is determined to be about 6 × 10 ¹⁹ atoms by general SIMS analysis.
s / cm ³ .

Subsequently, an argon-hydrogen mixed gas stream 11
At 00 ° C., a Mg-doped gallium nitride layer 103 a was deposited on the Mg-doped aluminum-gallium nitride layer 103 for 20 minutes. The gallium source was trimethylgallium, and the magnesium source used was an organic Mg compound similar to that used when growing the Mg-doped aluminum gallium nitride layer 103. Since the doping efficiency of magnesium tended to increase as the growth rate was reduced, about 3 nm /
Minutes. The layer thickness of the Mg-doped gallium nitride layer 103a was about 60 nm.

Each constituent layer 100 of the above-mentioned laminated structure 11
After the growth of a, 101, 102, 103, 103a,
The temperature of the substrate 100 is raised from 1100 ° C. to 950 in a state where ammonia gas is added to an equal volume mixed gas flow of argon and hydrogen.
The temperature was immediately dropped to ° C. From 1100 ° C. to 950 ° C., only the flow rate of hydrogen gas having a high thermal conductivity constituting the atmosphere was increased from 4 liters per minute to 8 liters per minute, and the cooling was performed forcibly in half without taking one minute. Substrate 100 at 950 ° C
Was lowered, only argon was used as the gas species flowing in the MOCVD reactor. The temperature was lowered from 950 ° C. to 650 ° C. at a rate of 10 ° C. per minute for 30 minutes. 650 ° C
The atmosphere in the MOCVD reactor from argon to
Cooled in a hydrogen atmosphere. It took about 45 minutes to reach about 30 ° C.

After cooling, the internal structure of the light emitting layer 102 was observed at an accelerating voltage of 200 KV by a normal section TEM technique using one fragment of the laminated structure 11 as a sample. FIG. 3 is a crystal lattice image when the light emitting layer in the first embodiment is imaged by a transmission electron microscope (TEM). The observation magnification is 2 × 10 ⁶ . In the drawing, it has been found that the light emitting layer 102 in the first embodiment has a multiphase structure composed of the main phase 201 and the substantially spherical and island-shaped subordinate phases 202. Island-like subordinate phase 20
2 was observed to be more present at the interface between the n-type gallium nitride layer 101 and the light emitting layer 102. The density of the dependent phase 202 obtained from the number of the dependent phases 202 in the imaging range is about 2 × 1
It was 0 ¹⁷ cm ^-3 . It was recognized that the indium composition was different between the main phase 201 and the dependent phase 202, and that the dependent phase 202 tended to have a higher indium concentration than the main phase 201. A dependent phase having an indium composition ratio of about 0.3 was also observed.

It is recognized that the dependent phase 202 has a strained layer 203 at the boundary with the surrounding main phase 201, and the dependent phase main body portion 202 a forming the center side and the strained layer 203 on the outer periphery thereof are formed.
And was composed of Substantially spherical dependent phase body portion 202
a has a diameter of about 25 to 35 ° (2.5 to 3.5 n
m). The size of the island-shaped dependent phase main body portion 202a was approximately 35 ° in width. In some cases, the angle difference in the arrangement direction of the lattice plane between the dependent phase main body portion 202a and the strained layer 203 was about 60 degrees. The strained layer 203 did not necessarily exist with a uniform thickness on the outer periphery of the dependent phase main body portion 202a, but was on average about 10 °. 25 to 35 in diameter or width
Strain layer 20 associated with dependent phase body portion 202a having
3 had a thickness (width) d of 8 to 13 °. About 10-15
The thickness d of the strained layer 203 associated with the relatively small dependent phase body portion 202a of Å was about 5 ° to about 7 °.

Using the above-mentioned laminated structure 11 as a base material, L
An ED was prepared. FIG. 4 is a diagram schematically showing a cross-sectional structure of the LED in the first embodiment, and is a cross-sectional view taken along line AA of FIG. 5, and FIG. 5 is a schematic plan view of the LED. In these figures, the LED 50 has a configuration in which electrodes are provided on the laminated structure 11 described above.

First, a region for forming the n-type pad electrode 109 was formed by plasma etching using a methane / argon / hydrogen mixed gas. On the surface layer of the n-type gallium nitride layer 101 exposed by etching, an n-type pad electrode 109 made of aluminum (Al) alone and having a diameter of 100 μm was formed by a normal vacuum deposition method.
The layer thickness was about 2 μm. Mg-doped gallium nitride layer 103a on the outermost surface of the portion left as a mesa
A p-type pad electrode 105 having a gold-beryllium (Au-Be) alloy on the side in contact with the Mg-doped gallium nitride layer 103a and a gold (Au) simple substance on the upper side is formed by a normal vacuum deposition method. And a total layer thickness of about 2 μm. The p-type pad electrode 105 was provided at a corner on the end face side of the chip facing the n-type pad electrode 109. On the surface of the Mg-doped gallium nitride layer 103a, a thickness of about 20 nm
The translucent gold thin film electrode 104 to be used is a p-type pad electrode 10
5 electrically connected to each other. Further, the gold thin film electrode 10
Only on the surface of No. 4, a translucent nickel (Ni) oxide thin film 104a having a thickness of about 10 nm and a high degree of insulation is formed.
Gold thin film electrode 104 and Mg-doped gallium nitride layer 103
The protective film was formed on almost the entire exposed surface of a.

In the LED 50 having the above structure, a DC voltage was applied between the n-type pad electrode 109 and the p-type pad electrode 105 to emit light. FIG. 6 shows measurement results of various light emission characteristics at that time. The description of FIG. 6 will be described later.

(Second Embodiment) After the laminated structure 11 of the first embodiment was formed, it was cooled under a temperature lowering condition partially different from that of the first embodiment. That is, 11 under the same conditions as in the first embodiment.
After cooling from 00 ° C to 950 ° C, 950 ° C to 800
The temperature was lowered at a rate of 7.5 ° C./min for 20 minutes. Then, it was kept at 800 ° C. for 15 minutes. Thereafter, the temperature was lowered from 800 ° C to 650 ° C at a rate of 10 ° C per minute. After the temperature was lowered to 650 ° C., only the hydrogen constituting gas supplied to the MOCVD reactor was cooled to room temperature. It took about 45 minutes to cool to about 30 ° C.

After cooling, the internal structure of the light emitting layer was identified by a cross-sectional TEM technique. The light emitting layer in the second embodiment has a multiphase structure composed of a main phase and a dependent phase, similarly to the light emitting layer 102 in the first embodiment. The dependent phase was found to have a strained layer at the boundary with the surrounding main phase. The indium concentration in the dependent phase was generally higher than that of the main phase, and the indium composition ratio of the main phase was estimated to be approximately 0.15. The main part of the dependent phase which forms the central side of the dependent phase is mainly a substantially spherical body, and its size is about 30 mm in diameter.
It was almost standardized. Further, the thickness of the strain layer around the main part of the dependent phase was also uniform at about 10 °. in this way,
In the second embodiment, the temperature of the cooling phase was lowered at 800 ° C. in the above-described cooling time including the waiting time of 15 minutes, so that the shape of the main body of the dependent phase could be made substantially spherical and almost uniform, and the thickness of the strained layer was also increased. It could be controlled uniformly.

(Comparative Example) After the laminated structure described in the first example was formed, it was naturally cooled from 1100 ° C. to room temperature. It took about 90 minutes to drop to about 30 ° C. Therefore, the average cooling rate was about 12 ° C./min. Following the prior art (see Japanese Patent Application Laid-Open No. 9-40490),
In a temperature zone of 1000 ° C. or lower, the inert gas atmosphere was made of argon. As in the first embodiment and the second embodiment, the operation of forming the atmosphere gas only from hydrogen in the temperature range of 650 ° C. or less was not performed.

The internal structure of the light emitting layer of the laminated structure cooled under the above conventional conditions was observed by a cross-sectional TEM technique. Section TE
On the M image, a linear black contrast, which is considered to be mainly caused by dislocations, is observed, but a spherical or island-like contrast, which indicates the existence of a dependent phase mainly caused by indium aggregation, is remarkably observed. Did not. From the number of substantially spherical or island-shaped contrasts in the imaging range, the density of the dependent phase was determined to be 1 × 10 ¹² cm ⁻³ or less. That is, it was difficult to clearly recognize that the light-emitting layer had a multi-phase structure.

Each laminated structure cooled under the conditions described in the second embodiment and the comparative example was processed in the same manner as in the first embodiment to produce LEDs, and a DC voltage was applied between the electrodes of each LED. And emitted light. FIG. 6 shows measurement results of various light emission characteristics at that time.

Referring to FIG. 6, the light emission characteristics of the LEDs in the first embodiment, the second embodiment, and the comparative example are compared.
There is no significant difference in emission wavelength between the EDs.
It became 50 nm. In addition, no remarkable difference was observed between the forward voltage when the forward voltage was set to 20 mA and the reverse voltage when the reverse current was 5 μA. On the other hand, from the comparison of the light emission output measured normally using a general integrating sphere, the LED in the second embodiment having the light emitting layer having the dependent phase accompanied by the almost uniform strain layer is found to be It exhibited the highest 2.1 mW. The light emission output of the LED in the comparative example was the lowest, 0.4 mW. The half-width (FWHM) of the main emission spectrum showed a further remarkable difference. The minimum value of the half width of the LED of the second example was 7 nm. The half value width of the LED of the first example was 9 nm, and the LED of the comparative example was 18 nm, which was the largest, and exhibited light emission lacking in monochromaticity.

In each of the above embodiments, the case where the present invention is applied to a light emitting diode (LED) has been described. However, the present invention relates to another light emitting element such as a laser diode (L).
The same can be applied to D).

[0050]

As described above, according to the nitride semiconductor light emitting device of the present invention, a multi-phase indium-containing group III nitride semiconductor composed of a main phase and a sub phase having different indium compositions is used. In the formed light emitting layer, the dependent phase is mainly composed of a crystal having a strained layer at the boundary with the surrounding main phase, so that the strained layer existing around the dependent phase has an emission intensity. Carrier that contributes to the increase in the number of electrons can be stably generated, and therefore, the crystal constituting the subordinate phase can effectively act as a quantized light emitting medium, and the nitride semiconductor including the light emitting layer Short-wavelength visible light output from the light-emitting element can be stably provided with high emission intensity and excellent monochromaticity.

[Brief description of the drawings]

FIG. 1 is an example of a crystal lattice image when a light emitting layer according to a nitride semiconductor light emitting device of the present invention is imaged by a transmission electron microscope (TEM).

FIG. 2 is a view showing a laminated structure according to a first embodiment of the present invention.

FIG. 3 shows a light-emitting layer according to the first embodiment, which is formed by a transmission electron microscope (T).
It is a crystal lattice image when imaged by (EM).

FIG. 4 is a diagram schematically showing a cross-sectional structure of the LED in the first embodiment, and is a cross-sectional view taken along line AA of FIG. It is a plane schematic diagram of LED.

FIG. 5 is a schematic plan view of an LED in the first embodiment.

FIG. 6 is a diagram showing various characteristics of the LED manufactured in each example.

[Explanation of symbols]

 Reference Signs List 2 light emitting layer 11 laminated structure 21 main phase 22 dependent phase 22a dependent phase main part 23 strained layer 50 LED 100 substrate 100a low temperature buffer layer 101 n-type gallium nitride layer 102 light emitting layer 103 Mg-doped aluminum / gallium nitride layer 103a Mg-doped nitride Gallium layer 104 Gold thin film electrode 104a Ni oxide thin film 105 P-type pad electrode 109 N-type pad electrode 201 Main phase 202 Dependent phase 202a Dependent phase main body part 203 Strain layer D Diameter (width) of sub phase main body part d Layer of strain layer Thick

Claims (3)

[Claims] 1. A nitride semiconductor light emitting device having a light emitting layer of an indium-containing group III nitride semiconductor layer having a multiphase structure composed of a main phase and a sub phase having different indium compositions, wherein the sub phase is A nitride semiconductor light emitting device mainly comprising a crystal having a strained layer at a boundary with a surrounding main phase. 2. The method according to claim 1, wherein said dependent phase has an overall size (D).
2. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is mainly formed of a crystal having a strained layer having a width of 0.5 × D or less. 3. 3. The nitride semiconductor light emitting device according to claim 1, wherein the number of the dependent phases having the strained layer accounts for 50% or more of the total number of the dependent phases.