JP3582587B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device in which a current diffusion layer is formed on a light emitting functional layer, and more particularly, to a semiconductor light emitting device in which reliability and electrical characteristics are improved to a high level.
[0002]
[Prior art]
A semiconductor light-emitting device including a light-emitting layer composed of an AlGaInP-based compound semiconductor can emit light in a red to green wavelength range with relatively high luminance. FIG. 1 shows a conventional semiconductor light emitting device provided with a light emitting layer made of an AlGaInP-based compound semiconductor. As shown in the figure, a semiconductor substrate 1 includes a substrate 2 made of n-type GaAs, a light emitting functional layer 3 made of an AlGaInP-based compound semiconductor, an n-type current blocking layer 4 made of n-type AlGaInP, A current diffusion layer 5 made of a P-type compound semiconductor such as GaP or A1GaAs. The light-emitting function layer 3 includes an n-type clad layer 8 made of n-type AlGaInP, a light-emitting layer (active layer) 9 made of AlGaInP, and a p-type clad layer 10 made of p-type AlGaInP. It is a thing. An anode electrode 6 and a cathode electrode 7 are formed on one and the other main surfaces of the semiconductor substrate 1. Here, the current diffusion layer 5 made of p-type GaP formed on the upper surface side of the base 1 is a layer also referred to as a window layer, and has a relatively low resistivity and a low resistance contact with the anode electrode 6. It is made of a material that is easily formed. For this reason, the current diffusion layer 5 has a function of spreading a current flowing from the anode electrode 6 to the cathode electrode 7 in the horizontal direction (in the plane direction of the element) in the current diffusion layer 5 and improving the light extraction efficiency. That is, the light emitted in the region below the anode electrode 6 in the light emitting layer 9 is blocked by the anode electrode 6 provided on the upper surface of the element, and it is difficult to take out the light well. Therefore, in order to improve the light extraction efficiency, it is desirable to spread the current as much as possible in the element plane direction so that light emission occurs in a region of the light emitting layer 9 on the outer peripheral side of the anode electrode 6. The current diffusion layer 5 made of p-type GaP has a function of satisfactorily spreading the current in the element plane direction so as to meet the above requirements.
The current diffusion layer 5 composed of the p-type light emitting layer 9 is substantially transparent to light having a wavelength of 550 to 650 nm emitted from the light emitting layer 9 composed of an AlGaInP-based compound semiconductor. 9 can emit the emitted light to the outside from the top surface of the element without absorbing much. In order to obtain a high-luminance semiconductor light-emitting device, it is important to efficiently extract light from the light-emitting layer 9 to the outside without greatly attenuating the inside of the device. The diffusion layer 5 is desirable.
[0003]
[Problems to be solved by the invention]
The current diffusion layer 5 composed of GaP or A1GaAs cannot obtain a good surface morphology when the crystal is grown at a relatively low temperature of about 800 ° C., so that the crystal is formed at a temperature higher than the crystal growth temperature of A1GaInP of the light emitting function layer. Need to grow. However, when the current diffusion layer 5 is crystal-grown on the light emitting function layer 3 at such a high temperature, the impurities (Zn, Mg, etc.) doped in the current diffusion layer 5 and the p-type cladding layer 10 are added to the light emitting layer 9. The element characteristics are degraded due to the diffusion, and the crystallinity is degraded at the current diffusion layer growth interface due to desorption of the crystal constituent atoms. For this reason, the reliability and electrical characteristics of the semiconductor light emitting device deteriorate.
[0004]
Therefore, an object of the present invention is to provide a semiconductor light emitting device capable of improving electrical characteristics and reliability.
[0005]
[Means for Solving the Problems]
The present invention for solving the above problems and achieving the above object provides a semiconductor substrate, a light emitting functional layer made of an AlGaInP-based compound semiconductor formed on one main surface of the semiconductor substrate, and one of the light emitting functional layers. A buffer layer formed on the main surface, and a current diffusion layer formed on one main surface of the buffer layer,
The buffer layer is made of Ga _x In _(1-x) P (x = 0.7 to 0.9), and has a light transmittance with respect to an emission wavelength of the light emitting functional layer;
A current blocking layer is formed on a part of one main surface of the light emitting functional layer ,
The semiconductor light emitting device, wherein the buffer layer is formed so as to cover a portion of one main surface of the light emitting function layer that is not covered with the current block layer and an upper surface and side surfaces of the current block layer. It is concerned.
Preferably, the current diffusion layer is made of AI _x Ga _(1-x) As (x = 0.7 to 0.9).
[0006]
【The invention's effect】
The invention of each claim of the present application has the following effects.
(1) When a buffer layer made of Ga _x In _(1-x) P (x = 0.7 to 0.9) is formed between the light emitting function layer and the current diffusion layer, crystal growth is performed at a relatively low temperature. Also, the surface morphology becomes better. As a result, the current diffusion layer can be formed well, and the reliability and electrical characteristics of the light emitting element can be improved.
_{(2) Ga x In (1} -x) P (x = 0.7~0.9) has good coverage against the underlying layer, good surface morphology - as possible out to obtain.
(3) The buffer layer made of Ga _x In _(1-x) P (x = 0.7 to 0.9) has good coverage with respect to the current block layer, and the top and side surfaces of the current block layer , So that an abnormal etching at the end of the current blocking layer can be prevented from occurring in an etching step or the like.
[0007]
Embodiment
Next, an embodiment of the present invention will be described with reference to FIG.
[0008]
As shown in FIG. 2, a semiconductor substrate 1a of a compound semiconductor light emitting device (light emitting diode device) according to one embodiment of the present invention includes a substrate 2 made of n-type GaAs, a light emitting functional layer 3 made of an AlGaInP compound semiconductor, and n An n-type current blocking layer 4 made of AlGaInP, a buffer layer 11 made of p-GaInP, and a current diffusion layer 5a made of AIGaAs are provided. An anode electrode 6 and a cathode electrode 7 are formed on one and the other main surfaces of the base 1a. The light-emitting functional layer 3 disposed on the substrate 2 includes an n-type clad layer 8 made of n-type AlGaInP, a light-emitting layer (active layer) 9 made of AlGaInP, and a p-type clad layer 10 made of p-type AlGaInP. These are sequentially laminated. The current blocking layer 4 is arranged in a central region on the upper surface of the p-type cladding layer 10. The p-type electrode, that is, the anode electrode 6, is disposed at the center of the upper surface of the current diffusion layer 5a. The n-type electrode, that is, the cathode electrode 7 is formed on the entire lower surface of the substrate 2.
[0009]
The light emitting device according to the embodiment of FIG. 2 differs from the conventional light emitting device of FIG. 1 in that a buffer layer 11 is interposed between a p-type cladding layer 10 and a current diffusion layer 5. Are formed in the same manner as in FIG. Buffer layer 11 in FIG. 2 _consists of _{Ga x In (1-x)} P. Here, x indicating the molar ratio between Ga and In is an arbitrary value in the range of 0.7 to 0.9. In this embodiment, since x is 0.8, the buffer layer 11 is made of a Ga _0.8 In _0.2 P compound semiconductor, and is formed thicker than the current blocking layer 4. The buffer layer 11 has a light-transmitting property with respect to the emission wavelength of the light-emitting layer 9, and has one main surface of the p-type clat layer 10 not covered with the current blocking layer 4 and the upper surface of the current blocking layer 4. It is formed so as to cover the side surface. Note that the thickness of the buffer layer 11 is desirably about 3 μm or less.
Since the light emitting device according to the present embodiment has a buffer layer, the current spreading layer 5 made of AIGaAs is not formed directly adjacent to the p-type cladding layer 10, and the current spreading layer 5 is made of a buffer layer made of p-type GaInP. It is formed on the p-type cladding layer 10 with the intermediary of 11.
With the buffer layer 11 interposed, the current diffusion layer 5a is not directly in contact with the upper surface of the p-type cladding layer 10, and the buffer layer 11 and the current blocking layer 4 are formed on the upper surface of the p-type cladding layer 10. In contact. _{Ga x In (1-x)} P (x = 0.7~0.9) buffer layer 11 made from a transparent layer or a light transmitting layer with respect to light emitted by the light-emitting layer 9 and the upper surface It can be said that the buffer layer 11 forms a part of the current diffusion layer together with the current diffusion layer 5 composed of the upper AIGaAs layer because the semiconductor layer is a low-resistance semiconductor layer similarly to the current diffusion layer 5a formed in FIG. When the buffer layer 11 is formed to be thin, the buffer layer 11 alone does not function well as a current spreading layer. Note that the composition ratio of Ga and In in the buffer layer 11 is not limited to the above, and can be arbitrarily set in the range of x = 0.7 to 0.9.
[0010]
Current spreading layer 5a _is preferably a _{AI x Ga (1-x)} As (x = 0.7~0.9), in this specific example is formed by _AI 0.8 _{Ga 0.2} As . The current diffusion layer 5a is a layer that is transparent to light emitted from the light emitting layer and is a low resistance semiconductor layer. Therefore, the current diffusion layer 5a can spread the current from the anode electrode in the plane direction of the device satisfactorily. Since the current diffusion layer 5a only needs to be a layer that has a property of transmitting light emitted from the light-emitting layer 9 and has low resistance, the composition ratio x of AI and the composition ratio (1-x) of Ga are as follows. The value is not limited to the above, and can be set to any value within the range of x = 0.7 to 0.9.
[0011]
When the light emitting device of FIG. 2 is formed, an n type AlGaInP for forming a light emitting function layer 3 is formed on a substrate 2 formed of an n type GaAs semiconductor layer by a well-known MOCVD (metal organic chemical vapor deposition). A type cladding layer 8, a light emitting layer (active layer) 9 made of AlGaInP, and a p-type cladding layer 10 made of p-type AlGaInP are formed, and further, an n-type AlGaInP layer forming the current blocking layer 4 is formed.
Next, the n-type AlGaInP layer is etched, and the n-type AlGaInP layer on the outer peripheral side of the substrate is selectively removed by etching, leaving the center side, thereby forming a current blocking layer 4. Note that the current block layer 4 is formed so as to substantially coincide with the anode electrode 6 in plan view.
Next, a buffer layer composed of a p-type Ga _0.8 In _0.2 P layer on the upper surface of the current blocking layer 4 and the light emitting functional layer 3 exposed outside the current blocking layer 4, that is, the p-type cladding layer 10 by MOCVD. 11 is formed. After the buffer layer 11, which was heated to _{H 2} (hydrogen) a carrier gas 4000ccm i.e. min per 4000 cm ³ and PH ₃ (phosphine) 180Ccm i.e. per minute per gas 180cm ³ flowed growth temperature (800 ° C.), TMG (trimethyl gallium) gas is flowed at 8 ccm, that is, 8 cm ³ per minute, TMI (trimethyl indium) gas is flowed at 53 ccm, that is, 53 cm ³ per minute, and DMZ (dimethyl zinc) gas is flowed at 12 ccm, that is, 12 cm ³ per minute. It is formed by growing crystals for 20 minutes. As a result, a buffer layer 11 having a thickness of about 1 μm is obtained.
Next, the V-group gas is switched to AsH3 (arsine) gas, which is about 95 ccm, ie, 95 cm ³ per minute, TMG gas 2 ccm, ie, 2 cm ³ per minute, and TMA (trimethylaluminum) gas is 13 ccm, ie, per minute. 13cm ^3, by performing crystal growth of a DMZ gas flow 13ccm i.e. per minute per 13cm ³ to about 2 hours, thereby forming a current diffusion layer 5a made of _AI 0.8 _{Ga 0.2} As with a thickness of about 6μm .
Finally, the anode electrode 6 and the cathode electrode 7 are formed on the upper and lower surfaces of the semiconductor substrate 1a formed as described above by well-known vacuum deposition or the like, thereby completing the semiconductor light emitting device of FIG.
[0012]
According to the semiconductor light emitting device of the present embodiment, a semiconductor light emitting device having high reliability and good electric characteristics can be obtained for the following reasons (1), (2) and (3).
_{(1) Ga x In (1} -x) P (x = 0.7~0.9) buffer layer 11 composed of, compared to AIGaAs like, at the same temperature as the growth temperature of the light-emitting functional layer 3 Good surface morphology can be obtained even by crystal growth. If the surface morphology of the buffer layer 11 is good, the current diffusion layer 5a composed of the relatively low temperature on the upper surface of the buffer layer _{11 AI x Ga (1-x} ) As (x = 0.7~0.9) Since the crystal can be satisfactorily grown, it is not necessary to grow the current diffusion layer at a temperature higher than that of the light emitting function layer 3 as in the prior art, and the reliability and the electrical characteristics at the growth interface of the current diffusion layer 5a are improved. Can be improved. _{Incidentally, Ga x In (1-x} ) P (x = 0.7~0.9) from forming a thick buffer layer 11 made of a buffer layer 11 by omitting the current diffusion layer 5a formed on the upper surface May also be configured to also serve as the current diffusion layer 5a. However, such a structure reduces reliability. The reason is not necessarily _clear, when forming a thick buffer layer 11 made of _{Ga x In (1-x)} P (x = 0.7~0.9), albeit at the growth essentially lattice mismatch It is considered that the difference in lattice constant between GaAs of the substrate 2 and the GaAs in the process of lattice relaxation acts as a tensile stress on the buffer layer 11, so that the crystallinity is easily deteriorated. Such a problem does not occur in the light emitting device of the present embodiment.
(2) Since the current diffusion layer 5a is laminated on the GaAs substrate 2 via the buffer layer 11 which is a GaInP layer which is a lattice mismatching system, the current diffusion layer 5a made of AIGaAs is formed on the GaAs substrate 2 with a lattice mismatch. Crystal growth can be performed as a matching system. Therefore, the stress applied to the current diffusion layer when the current diffusion layer is epitaxially grown can be reduced.
_{(3) Ga x In (1} -x) P (x = 0.7~0.9) buffer layer 11 composed of _{the, AI x Ga (1-x} ) As (x = 0.7~0. 9) The coverage with respect to the underlying layer is better than that of the current diffusion layer 5a composed of the above. Thus, through the buffer layer 11 made of _{Ga x In (1-x)} P (x = 0.7~0.9) on the upper surface of the p-type cladding layer _{10 AI x Ga (1-x} ) As (x = By forming the current spreading layer 5a of 0.7 to 0.9), the occurrence of pits and the like in the current spreading layer 5a can be satisfactorily suppressed, and the surface morphology of the layer can be satisfactorily obtained. In particular, when the current blocking layer 4 is formed, the crystallinity tends to deteriorate in the growth region on the end side of the current blocking layer 4, but the crystallinity in this region is also improved by interposing the buffer layer 11. it can. As described above, if the coverage can be improved, it is possible to prevent the occurrence of abnormal etching at the end of the current blocking layer 4 in the etching step or the like, and to improve the process yield.
[0013]
[Modification]
The present invention is not limited to the above embodiment, and for example, the following modifications are possible.
(1) A well-known DBR layer in which, for example, an AlGaInP layer and GaAs are alternately arranged can be formed between the n-type GaAs substrate 2 and the light emitting function layer 3. The DBR layer is a distribution formed by providing a plurality of superlattice layers having different effective refractive indices, each of which is composed of a superlattice layer having a low refractive index and a superlattice layer having a high refractive index. It is a Bragg reflecting film (Distributed Bragg Reflectors) for reflecting light from the light emitting layer 9 toward the back surface of the substrate 2 to the front surface side.
(2) The light emitting function layer 3 can have a well-known multiple quantum well structure.
(3) The n-type cladding layer 8 and the p-type cladding layer 10 can be formed of a plurality of layers.
(4) A structure in which the current block layer 4 is omitted can be provided. Further, another semiconductor layer can be formed on the semiconductor substrate 1a.
(5) The cathode electrode 7 can be formed on the extended upper surface of the substrate 1.
(6) The current diffusion layer 5a can be made of GaP or the like.
(7) The buffer layer 11 and the current diffusion layer 5a can be alternately stacked a plurality of times.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a conventional semiconductor light emitting device.
FIG. 2 is a sectional view showing a semiconductor light emitting device according to the embodiment;
[Explanation of symbols]
1a Semiconductor substrate 2 Substrate 3 Light emitting function layer 4 Current blocking layer 5a Current diffusion layer 6 Anode electrode 7 Cathode electrode

Claims (2)

A semiconductor substrate, a light emitting function layer made of an AlGaInP-based compound semiconductor formed on one main surface of the semiconductor substrate, a buffer layer formed on one main surface of the light emitting function layer, and one of the buffer layers And a current diffusion layer formed on the main surface,
The buffer layer is made of Ga _x In _(1-x) P (x = 0.7 to 0.9), and has a light transmittance with respect to an emission wavelength of the light emitting functional layer;
A current blocking layer is formed on a part of one main surface of the light emitting functional layer ,
The semiconductor light emitting device according to claim 1, wherein the buffer layer is formed so as to cover a portion of one main surface of the light emitting functional layer that is not covered with the current block layer and an upper surface and side surfaces of the current block layer . The current diffusion _{layer, AI x Ga (1-x} ) As semiconductor light emitting device according to claim 1, characterized in that it consists of (x = 0.7~0.9).

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