JPH08125285A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE: To improve a characteristic and reliability of a light-emitting element by being provided with an active layer consisting of AlGaInP having a thickness under a specific width, second and third clad layers consisting of AlGaInP at the upper and lower sides of the active layer having a thickness below a specific width and first and fourth clad layers consisting of AlGaAsP besides having a current blocking layer. CONSTITUTION: A first clad layer 103 consisting of a first conductive type AlGaAsP group compound is laminated on a substrate 101 provided on a buffer layer 102. Next, a second clad layer 104 consisting of an AlGaInP group compound and having a thickness below 0.05μm is laminated whereon an active layer 105 consisting of the first or second conductive AlGaInP or GaInP having a thickness under 0.1μm is laminated. Next, a third clad layer 106 consisting of the second conductive type AlGaInP group compound and having a thickness below 0.5μm is laminated and further a fourth clad layer 107 consisting of the AlGaAsP group compound is laminated. And, a position of a current blocking layer 108 constricting a current to the active layer 105 is not particularly limited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using AlGaInP-based and AlGaAsP-based semiconductor materials.

[0002]

2. Description of the Related Art As an example of a conventional semiconductor laser diode (LD) using an AlGaInP-based semiconductor material, there is a structure as schematically shown in FIG. That is, in FIG. 2, 201 is an n-type GaAs substrate, and 202 is
It is a clad layer made of n-type AlGaInP formed on the substrate 201. 203 is an active layer made of AlGaInP. Reference numeral 204 is a cladding layer made of p-type AlGaInP. That is, the AlGaInP active layer 2
The mixed crystal ratio is set so that the energy gap of 03 is smaller than the energy gap of the AlGaInP cladding layers 202 and 204, thus forming a double hetero structure. 206 is a contact layer.

Reference numeral 205 is a current blocking layer made of GaAs. The current blocking layer 205 is provided for the purpose of so-called current constriction in order to obtain a current density required for laser oscillation. The layer 205 is formed by selectively etching the layer 204 to form a ridge, and then selectively growing the layer 204 using an amorphous film such as SiNx.

[0004]

Problems to be Solved by the Invention AlGaInP or A
In comparison with AlGaAsP or AlGaAs (hereinafter collectively referred to as AlGaAsP-based compound), lInP (hereinafter collectively referred to as AlGaInP-based compound) has drawbacks such as high resistivity and large thermal resistance. However, there are problems such as increasing the operating voltage of the element and increasing heat generation, which is a major problem in improving the characteristics and reliability of the element. In particular, when the current is constricted or the emission density is increased like the semiconductor laser, the above problems become more serious.

Further, zinc (Zn) is generally used as a dopant for the cladding layer of a p-type AlGaInP-based compound, but since the activation rate of Zn is low, high-concentration doping is used to reduce the resistivity. Need to do. However, in this case, Zn that has not been activated may diffuse in the AlGaInP-based compound crystal at a high speed during the growth, and the pn junction position may be largely displaced to the n side from the light emitting layer. In this case, the current-voltage characteristics may be abnormal, or the threshold current of the laser may be increased. Z from such a p-type AlGaInP-based compound layer
The n diffusion becomes remarkable as the layer thickness of the p-type AlGaInP-based compound layer increases. Further, when the thickness of the light emitting layer is comparatively thin like a laser, the current-voltage characteristics are likely to be abnormal due to Zn diffusion. Si having a small diffusion coefficient is effective for the n-type AlGaInP-based compound layer.

Usually, when a double hetero structure is used, in order to sufficiently confine carriers and light in the active layer,
The film thickness of the clad layer is required to be about 1 to 2 μm.
When an AlGaInP-based compound is grown by metalorganic vapor phase epitaxy, an organic metal as a group III source and a P as a group V source are used.
It is necessary to make the supply molar ratio (V / III) with H ₃ very large. For this reason, there are problems that the growth rate cannot be increased so much and that the cost of the growth raw material becomes considerably higher than that of the AlGaAs compound. Especially in the case of a large-scale apparatus for mass production, where a large number of wafers can be grown simultaneously, other problems such as harm removal become more serious.

[0007]

Means for Solving the Problems Therefore, the present inventors have proposed A
In a semiconductor light emitting device having an active layer made of 1GaInP or GaInP, the Zn-doped p-type AlGaInP-based compound clad layer is thinned to the extent that the device characteristics of the light emitting device are not deteriorated, and Zn is diffused into the active layer and the n-side clad. However, if the thickness of the AlGaInP-based compound clad layers above and below the active layer is reduced, carriers and light will not be confined sufficiently and the device characteristics will be deteriorated. It was found that an AlGaAsP compound having a band gap and a refractive index can be used as a substitute. In addition, n-type AlGaAsP
AlGaIn having similar carrier concentration
Since Zn diffusion is less likely to occur than that of a P-based compound, the thinner the n-type AlGaInP-based compound clad is Zn.
From the viewpoint of mass production, it is also effective to prevent the shift of the pn junction position due to diffusion, and that the thinning of the AlGaInP-based compound cladding layer is also effective to reduce the operating voltage and thermal resistance. The inventors have found that it is more effective to make the AlGaInP-based compound layer as thin as possible and use a large amount of AlGaAsP-based compound from the viewpoints of growth time, raw material cost, detoxification, etc., and arrived at the present invention. That is, the gist of the present invention is the first conductivity type AlGaAsP or AlGa.
A first clad layer made of As, a second clad layer made of AlGaInP or AlInP of a first conductivity type and having a thickness of 0.5 μm or less, which is adjacent to the first clad layer;
Adjacent to the clad layer of AlG of the first or second conductivity type
An active layer made of aInP or GaInP and having a thickness of less than 0.1 μm, and a second conductivity type AlGa adjacent to the active layer.
The active layer comprises a third clad layer made of InP or AlInP and having a thickness of 0.5 μm or less, and a fourth clad layer made of AlGaAsP or AlGaAs of the second conductivity type, which is adjacent to the third clad layer. The semiconductor light emitting device is characterized by having a current blocking layer for confining a current to the semiconductor light emitting device.

The present invention will be described in more detail below. The semiconductor light emitting device of the present invention comprises a first clad layer made of a first conductivity type AlGaAsP compound, and a thickness of 0.5 μm or less made of a first conductivity type AlGaInP compound adjacent to the first clad layer. Of the second clad layer and adjacent to the second clad layer, the first or second conductivity type AlGaIn
An active layer of P or GaInP having a thickness of less than 0.1 μm and a second conductivity type AlGaInP adjacent to the active layer.
A third clad layer having a thickness of 0.5 μm or less, which is made of a system-based compound, and a second conductivity type AlG adjacent to the third clad layer.
It is characterized in that it has a fourth cladding layer made of an aAsP-based compound, and has a current blocking layer for confining the current to the active layer. The content ratio of the constituent elements in each layer of the semiconductor light emitting device of the present invention may be determined in consideration of the lattice matching between the substrate and each layer. The element of FIG. 1, which is an example of a mode in which the light emitting device of the present invention is realized as a laser diode, will be described below.

FIG. 1 shows an example of the semiconductor device of the present invention.
It is explanatory drawing of the apparatus manufactured in the Example. When manufacturing the device of the present invention, it is usually constructed on a single crystal substrate. The substrate 101 is not particularly limited, but a GaAs substrate is usually used. On the substrate, 2μ is used to prevent the defects of the substrate from being introduced into the epitaxial growth layer.
It is preferable to use the buffer layer 102 having a thickness of about m or less. Then, the first and second clad layers, the active layer, and the third and fourth clad layers of the present invention are laminated in this order on this buffer layer, and the current to the active layer is constricted to reduce the current density in the active layer. A current blocking layer is provided for improvement. First
The clad layer 103 is made of AlGaAs of the first conductivity type.
It is a P-based compound, and its thickness is usually preferably 0.3 to 3 μm. And the more preferable thickness of the first cladding layer is 0.5 μm or more as a lower limit and 1.5 μm as an upper limit.
m. The carrier concentration is 1 × 10
^{The range of 17} cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ is preferable, and particularly preferable is 2 × 10 ¹⁷ cm ⁻³ as the lower limit and 2 as the upper limit.
It is in the range of × 10 ¹⁸ cm ^-3 .

A second clad layer 104 of a first conductivity type AlGaInP compound having a thickness of 0.5 μm or less is laminated on the first clad layer. The more preferable lower limit of the thickness of this layer is 0.01 μm or more,
The upper limit is 0.3 μm. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 2 × 10 ¹⁷ as the lower limit.
cm ⁻³ , and the upper limit is in the range of 2 × 10 ¹⁸ cm ⁻³ .

A first or second layer is formed on the second cladding layer.
An active layer 105 made of conductive type AlGaInP or GaInP and having a thickness of less than 0.1 μm is stacked. As the active layer, an active layer having a quantum well structure may be used. The carrier concentration of the active layer is not particularly limited, and rather, the fact that the active layer is in an undoped state (even in this case, it is slightly of the first or second conductivity type) does not affect the performance of the device. It is more preferable from the viewpoint of stabilization.

A second conductivity type A is formed on the active layer.
A third clad layer 106 made of a 1GaInP-based compound and having a thickness of 0.5 μm or less is laminated. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , and particularly preferably, the lower limit is 2 × 10 7.
The range is ¹⁷ cm ^-3 and the upper limit is 2 × 10 ¹⁸ cm ^-3 .

Further, a fourth clad layer 107 made of a second conductivity type AlGaAsP-based compound is laminated on the third clad layer. And its thickness is 0.3-3
A range of μm is preferred, and a more preferred range is 0.5 μm as a lower limit and 1.5 μm as an upper limit. The carrier concentration is 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ c
The range of m ^-3 is preferable, and the lower limit is particularly preferably 2
The range is × 10 ¹⁷ cm ^-3 and the upper limit is 2 × 10 ¹⁸ cm ^-3 .

The current blocking layer 108 used in the present invention is
This layer is provided for the reason that the current density in the active layer is increased without changing the current flowing through the device. The position of the current blocking layer is not particularly limited. However, since it is easy to obtain a flat active layer or a high-quality epitaxial growth layer, it may be located on the opposite side of the substrate from the active layer.
It is preferable in the case of vapor phase growth such as the CVD method.

Further, the presence on the side surface of the active layer is the best from the viewpoint of current confinement. However, a structure in which the current blocking layer spreads immediately before the third cladding layer or in a part of the third cladding layer is more preferable because it is likely to damage the active layer. The conductivity type of the current blocking layer is preferably a high resistance undoped layer or the conductivity type opposite to that of the adjacent clad layer. Also, if it is too thin, it may interfere with current blocking,
The thickness is preferably 0.1 μm or more, more preferably 0.5 μm or more, and may be selected from the range of about 0.1 to 3 μm in consideration of the size as an element. In order to improve the characteristics of the laser device, it is more preferable that the current blocking layer is made of AlGaAsP or AlGaAs, and the refractive index of the current blocking layer is smaller than the refractive index of the ridge structure portion that serves as a current path. preferable.

As the kind of dopant for the above-mentioned cladding layer, carbon is preferable as a doping impurity when the p-type layer is an AlGaAsP-based compound layer, and when the p-type layer is an AlGaInP-based compound, doping is performed. Beryllium and / or magnesium are preferred as impurities. Silicon is preferable as the n-type doping impurity.

As the other layers, the cap layer 10 is used.
9, the contact layer 110, the protective layer 112, etc. may be manufactured by a conventional method. Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded.

[0018]

EXAMPLES Examples of the present invention will be described in detail below. In this embodiment, the MOVPE method, which is excellent in controllability of film thickness, composition and mass productivity, is used as the crystal growth method. The source gases used were trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TM).
I), phosphine (PH ₃ ), and arsine (AsH ₃ ), and hydrogen (H ₂ ) gas highly purified by purification was used as a carrier gas.

The laser diode of the present invention as shown in FIG.
The epitaxial wafers used for manufacturing
It was manufactured by the following procedure. First, n-type GaAs (100) substrate
N-type GaAs buffer layer 102 (thickness: 0.
5 μm), n-type Al_0.7Ga _0.3As first clad layer 1
03 (thickness 1.0 μm), n-type (Al_0.7Ga_0.3)
_0.5In_0.5P second cladding layer 104 (thickness 0.2 μ
m), the active layer 105 is Ga _0.5In_0.5P (0.06μ
m), p-type (Al_0.7Ga_0.3)_0.5In_0.5P third
Rad layer 106 (thickness 0.2 μm), p-type Al_0.7Ga
_0.3As clad layer 107 (thickness 1.0 μm), p-type G
Sequential growth of aAs cap layer 109 (thickness 0.2 μm)
(Fig. 3).

Next, in order to form a ridge, a SiNx film 111 was formed in the portion where the ridge is to be formed. Subsequently, the fourth clad layer 107 and the cap layer 109 were etched, and the etching was stopped at the surface of the third clad layer 106. As a result, a ridge as shown in FIG. 4 was formed. At this time, phosphoric acid-hydrogen peroxide system, tartaric acid-hydrogen peroxide system, or the like is used for etching the GaAs cap layer and the AlGaAs cladding layer. In these etchings, the etching rate of AlGaInP is AlGa
Since it becomes much slower than As, the layer thickness of the portion outside the ridge can be determined with good controllability.

The wafer on which the ridge was formed was placed in an MOCVD apparatus and, as shown in FIG. 5, n-type Al _0.8 Ga was used.
_{Using the 0.2} As layer 108 as a current blocking layer, the cap layer 10
Side of ridge including 9 and etched layer 107
0.8 μm is grown on top by MOCVD. Further, an n-type GaAs layer 11 is formed on the current blocking layer 108 as a protective layer.
2 was grown to 0.2 μm. At this time, Al _0.8 Ga
_A small amount of HCl gas was introduced into the growth space during the growth until the deposition of polycrystal on the _0.2 As layer SiNx film was suppressed.

As shown in FIG. 1, after removing the SiNx film 111, the p-type GaAs contact layer 110 was grown to a thickness of 2 μm, and the production of the epitaxial wafer of the present invention was completed. After vapor-depositing electrodes on the obtained epitaxial wafer, dicing was performed and a Fabry-Perot surface was formed by cleavage to form a laser diode. The threshold current was very low at 20 mA, and the in-plane uniformity was very good at about ± 5% for a 2-inch wafer. Further, by using AlGaAs for the ridge as compared with the conventional AlGaInP ridge, the device resistance can be reduced to about half.

The crystal growth conditions in the above embodiment are as follows: growth temperature 650 to 750 ° C., pressure 10 ² hPa, V / III ratio 25 to 50 (AlGaAs) and 500 to 750 (Al).
GaInP, GaInP), growth rate 1-5 μm / hr
(AlGaAs) and 0.5 to 2 μm / hr (AlGa
InP, GaInP). Although an n-type substrate is used on the substrate side in the above embodiments, a p-type substrate may be used to invert the conductivity type of each layer having the above structure to produce an epitaxial wafer. Further, the crystal growth method is not limited to the MOVPE method, and the present invention is also very effective in vapor phase growth methods such as the MBE method and the CBE method.

Since the thickness of the active layer is relatively thin in a semiconductor laser (usually 0.1 μm or less), if an impurity having a large diffusion coefficient such as zinc and selenium is used as a dopant, the dopant in the clad layer becomes active. Problems such as passing through the layer and diffusing to the layer on the opposite side, which greatly deteriorates the laser characteristics and greatly impairing reproducibility, are likely to occur. As a method for suppressing Zn diffusion, an attempt was made to increase the carrier concentration in the n-side cladding, but the device characteristics were deteriorated due to deterioration of crystal quality such as poor surface morphology and increase of non-radiative centers.
Therefore, as in the present invention, by making the thickness of the AlGaInP clad layer as thin as possible, the total amount of impurity diffusion can be reduced, and extra doving for preventing diffusion is unnecessary. Therefore, the carrier concentration of the n-type cladding layer can be suppressed to 1 × 10 ¹⁸ cm ⁻³ or less, and the crystal quality and device characteristics can be improved.

If the active layer is made of an ultra-thin film such as a quantum well structure, the above-mentioned suppression of the diffusion of impurities becomes more and more necessary. Therefore, in the present invention, carbon is used as a doping impurity of the p-type AlGaAsP-based compound clad layer, and p-type AlG
Beryllium or magnesium is used as a doping impurity for the aInP-based compound cladding layer, and n-type AlGaAs is used.
By using silicon as a doping impurity for the P-type compound clad layer and the n-type AlGaInP-type compound clad layer, the impurity diffusion can be further reduced, and the yield and reproducibility of device fabrication can be greatly improved.

The AlGaAsP-based compound is AlGaI.
Compared with nP-based compounds, it also has advantages such as low resistivity and low thermal resistance. By using an AlGaAsP-based compound for the ridge portion formed due to current constriction, conventional device structure can be obtained. In comparison, the operating voltage and heat generation of the device could be reduced. As a result, the characteristics and reliability of the device could be improved.

Further, suppression of a decrease in bandgap due to ordering of atomic arrangement peculiar to AlGaInP compounds,
That is, to suppress the emission wavelength from becoming longer, or to improve and stabilize the surface morphology, the plane orientation should be (100).
It is effective to use a GaAs substrate of the first conductivity type that is tilted by 5 to 25 degrees in the [011] direction. Further, the reduction of the Al composition of the light emitting layer is important in terms of the reliability and life of the device, which can be easily achieved by using a GaAsP substrate. At this time, an AlGaAsP clad may be used to obtain lattice matching.

Further, according to the present invention, it is possible to greatly reduce the growth time and the cost of raw materials and to reduce the burden on the apparatus such as the removal of harm, and it becomes possible to perform stable production by a large-scale mass production apparatus capable of simultaneously growing a large number of sheets. .

[0029]

According to the present invention, AlGaInP or G
By optimizing the structure of the clad layers sandwiching the active layer made of aInP, the characteristics and reliability of the light emitting element can be improved and the raw material cost can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a light emitting device of the present invention.

FIG. 2 is an explanatory diagram showing an example of a conventional light emitting element.

FIG. 3 is a diagram for explaining a method for manufacturing a light emitting device according to the present invention.

FIG. 4 is a diagram for explaining a method for manufacturing a light emitting device of the present invention.

FIG. 5 is a diagram for explaining a manufacturing method of the light emitting device of the present invention.

[Explanation of symbols]

 101 substrate 102 buffer layer 103 first clad layer 104 second clad layer 105 active layer 106 third clad layer 107 fourth clad layer 108 current blocking layer 109 cap layer 110 contact layer 111 SiNx film 112 protective layer

Claims (9)

[Claims] 1. A first conductivity type AlGaAsP or AlG
a first clad layer made of aAs, and a first conductivity type AlGaInP or AlInP adjacent to the first clad layer.
And a second clad layer having a thickness of 0.5 μm or less and adjacent to the second clad layer, and having a first or second conductivity type Al.
An active layer made of GaInP or GaInP and having a thickness of less than 0.1 μm, and a second conductivity type AlG adjacent to the active layer.
A third clad layer made of aInP or AlInP and having a thickness of 0.5 μm or less, and a second clad layer adjacent to the third clad layer.
Fourth type of conductivity type AlGaAsP or AlGaAs
A semiconductor light emitting device comprising a clad layer and a current blocking layer for confining a current to the active layer. 2. The first clad layer and / or the fourth clad layer has a ridge structure made of AlGaAsP or AlGaAs, and a current blocking layer is provided on the left and right sides of the ridge structure. Semiconductor light emitting device. 3. The semiconductor light emitting device according to claim 1, wherein the current blocking layer has a conductivity type opposite to that of the clad layer in contact with the current blocking layer or a high resistance semiconductor. 4. The semiconductor light emitting device according to claim 1, wherein the current blocking layer is in contact with a ridge sidewall made of AlGaAs and a bottom surface made of AlGaInP or AlInP. 5. The current blocking layer is AlGaAsP or A
5. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is made of 1 GaAs, and the refractive index of the current blocking layer is smaller than the refractive index of the ridge structure portion serving as a current path. 6. The cap of an n-type layer of the cladding layer.
Rear concentration is 1 × 10 ¹⁸cm^-3The following are claims 1 to 5.
The semiconductor light emitting device according to any one of 1. 7. The first clad layer and the fourth clad layer, wherein the p-type layer is an AlGaAsP or AlGaAs layer, and the p-type layer contains carbon as a doping impurity. The semiconductor light-emitting device described. 8. The second clad layer and the third clad layer, wherein the p-type layer is AlGaInP or AlInP, and the p-type layer contains beryllium and / or magnesium as a doping impurity. 5. The semiconductor light emitting device according to any one of 1. 9. The semiconductor light emitting device according to claim 1, wherein silicon is used as the n-type doping impurity.