JP3499749B2 - Semiconductor light emitting device and method of manufacturing the same - Google Patents

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, and more particularly to a semiconductor light emitting device such as a semiconductor laser or a light emitting diode using a steam oxidation layer of a semiconductor containing aluminum (Al), and a method for manufacturing the same.

[0002]

2. Description of the Related Art A semiconductor laser (laser diode: LD) and a light emitting diode (LED) are
In the field of optical communication using infrared rays and visible light,
CD (compact disc) and DVD (digital versatile di
It is being widely used in consumer and commercial fields such as optical disc systems such as sc) and bar code readers.

For example, taking the field of optical communication as an example, in recent years, research for reducing the cost of an optical transmission system has been actively conducted with the aim of realizing an optical subscriber system, but a plastic having a large diameter is used. Fiber (plastic opti
If you use a cal fiber (POF), it will be an LD that becomes a transmission light source.
The LED and the optical fiber can be directly optically coupled without using a lens, and the number of parts can be reduced. In addition, the tolerance regarding the optical axis alignment is large,
Since the medium itself is cheap, it is possible to construct a low-cost optical link. Currently available and inexpensive PO
F has PMMA (PolyMethyl MethAcrylate) as a core material, and has a transmission loss window region near a wavelength of 650 nm (red). Therefore, the wavelength is 650 nm
There is an urgent need to develop a red light source. Conventionally, LEDs (Light emitting diodes) are used exclusively for optical links using visible light.
Has been used, but the upper limit of its transmission speed is 100 at most.
It is about Mbps. Therefore, in higher speed data transmission applications, LDs are needed as light sources. However, the red LD has a history of being developed for optical recording applications, and many studies and improvements must be made in order to use it for optical communication applications. In optical recording LDs, high output is a major development point, whereas in communication LDs,
From the viewpoint of high-speed driving, lower threshold is an essential development point.

That is, the characteristics required for these LDs include low current operation, high speed response, and long life. In order to satisfy these characteristics, the following structural and manufacturing methods have been generally adopted.

FIG. 5 is a schematic sectional view showing the structure of the main part of a conventional LD. That is, on a semiconductor substrate 101 such as n-type GaAs, a lower clad layer 102 having a low refractive index made of n-type AlGaAs or the like, an active layer 103 such as GaAs,
After laminating the low-refractive-index upper clad layer 104 made of p-type AlGaAs or the like, mesa etching is performed as shown in the figure, and the periphery of the mesa is filled with a low-refractive-index block layer 105 made of n-type AlGaAs. In addition, p
Embedded in the mold contact layer 106, the p-side electrode 107, n
Each side electrode 108 is formed.

The operation of the LD shown in FIG. 5 will be described.
The holes injected from the side electrodes 107 are the contact layers 106.
And the blocking layer 105 are squeezed due to the difference in energy level between them and injected into only the active layer 103.
It recombines with the electrons injected from 08 and emits light.
As the width of the active layer 103 embedded in the block layer 105 is narrower, the recombination efficiency is improved, and light emission can be obtained with a small injection current. Further, since the refractive index of the block layer 105 is smaller than that of the active layer, light is confined (guided) in the active layer, and the efficiency of stimulated emission is improved. That is, the block layer 105 contributes to the low current operation of the LD by confining both current and light in the active layer.

The same current constriction structure can be applied to an LED, and an LED having a high current injection efficiency can be realized.

[0008]

However, in a buried heterostructure (BH) as shown in FIG. 5, a double heterostructure including a clad layer and an active layer is processed into a mesa shape, and a block layer is further formed. There is a problem that it is necessary to perform buried growth, the manufacturing process is complicated, and stability and reproducibility are not sufficient.

On the other hand, the application field of optical communication will be described in more detail as follows. That is, in the 650 nm band InGaAlP-based red laser used for POF, since it is extremely difficult to bury and regrow with a quaternary material with respect to the quaternary mesa, conventionally, this process is relatively easy to bury the mesa with GaAs. Current constriction and transverse mode control were performed. This structure is SBR (Se
lectively buried ridge) structure.

However, since this GaAs buried layer has a strong absorption property with respect to the laser oscillation wavelength, a waveguide having a very large propagation loss is formed. Therefore, since absorption is large for a higher-order mode with a large exudation from the guide region, its growth is suppressed and, as a result, the fundamental mode is selected, but it is possible to reduce the threshold value. There was a problem that there was a limit.

Further, in order to lower the threshold value, a method of reducing the injection current while keeping the current density while narrowing the stripe width is taken, but in the SBR structure, when the stripe width is reduced, the light The confinement deteriorates and the light becomes more GaA
Since it leaks to the s layer, the internal loss increases, which not only offsets the effect of stripe width constriction, but also raises the problem of increasing the threshold value.

Further, since the SBR structure has a large reactive current in the first place, when the stripe width is narrowed, the ratio of the reactive current to the injection current increases, which also becomes an obstacle to lowering the threshold value. Furthermore, since the conventional SBR structure has the characteristics of an absorption guide instead of an actual refractive index guide, lateral mode control is unstable, and kinks occur especially at high output, and the refractive index changes due to internal temperature rise. There is also a problem that the lateral mode shape is apt to change due to, and as a result, the output is dependent on the internal temperature.

The present invention has been made based on the recognition of such various problems. That is, it is an object of the present invention to provide a light emitting device which can surely confine a current with a simple structure and can achieve a lower threshold value and actual refractive index mode control. Further, by increasing the efficiency and lowering the threshold of the 650 nm band InGaAlP-based red semiconductor light emitting device, the POF has a small transmission loss, and
The purpose is to greatly contribute to high-speed optical transmission using F.

[0014]

According to the present invention, an oxide layer formed by selectively oxidizing a semiconductor layer containing aluminum is used as a current blocking region or a protective film.

That is, in the semiconductor light emitting device of the present invention, an active layer, a first layer provided on the active layer and containing aluminum, and a mesa laminated aluminum layer on the first layer. A second layer containing the first layer,
And an oxide layer formed by oxidizing the first layer exposed on the bottom surface of the mesa and the second layer exposed on the side surface of the mesa, respectively. It is characterized by having a wedge-shaped current block region whose thickness decreases toward the inside of the mesa.

That is, the Al oxide layer formed on the bottom surface of the mesa of the mesa-shaped semiconductor substrate is formed so that the thickness increases at the bottom of the mesa and extends like a wedge into the mesa.

Further, the manufacturing method thereof includes a step of laminating an active layer on a semiconductor substrate, a step of laminating a first semiconductor layer containing aluminum on the active layer, and the first step.
Laminating a second semiconductor layer containing aluminum on the semiconductor layer, partially exposing the first semiconductor layer by removing the second semiconductor layer, and in a steam atmosphere. And oxidizing the first semiconductor layer and the second semiconductor layer respectively by increasing the temperature. Here, it is desirable to selectively cause the oxidation.

More specifically, for example, at least a layer of Al _X Ga _1-X As and Al _Y Ga _1-Y As (0.7≤X <Y≤1) is formed on the surface of the semiconductor substrate including the active layer. After sequentially laminating and selectively removing the layers up to the Al _Y Ga _1-Y As layer, a heat treatment is performed in a steam atmosphere to oxidize.

The second semiconductor light emitting device of the present invention is
In a InGaAlP-based light emitting device, a DH (Double heterostrand) using InGaAlP-based active layer and clad layer is used.
ucture) forming a selective oxidation layer containing AlAs on the structure,
Further, it is characterized in that the AlGaAs layer constitutes a current injection path.

That is, an active layer made of InGaAlP semiconductor and InGaAlP provided on the active layer.
A clad layer made of a system semiconductor, an aluminum-containing selective oxidation layer provided on the clad layer, and an AlGaAs semiconductor layer provided on the selective oxidation layer. It is characterized by having a current block region formed by being oxidized from, so that the element resistance can be reduced and the temperature characteristics can be improved. That is, quaternary (InG) is formed on the selective oxidation layer containing AlAs.
By providing a current injection part made of AlGaAs that is easier to obtain a lower resistance than aAlP), the p-type resistance is reduced, and finally a low resistance and low threshold semiconductor light emitting device suitable for high speed modulation is provided. You can Furthermore, InG
Selective etching of aAlP-based and AlGaAs-based enables mesa formation in a single process,
Cost reduction is also possible.

Here, the selective oxidation layer and the AlGaA
The s-semiconductor layer is laminated in a ridge shape on the clad layer and is exposed on the side surface of the ridge.
It is characterized in that an oxide layer is formed on the side surface of the As-based semiconductor layer. That is, Al is injected into the current injection portion on the selective oxide layer.
Since the GaAs layer is used, in the case of the mesa or ridge structure, not only the selective oxidation layer but also the side surfaces of the mesa are oxidized by the selective oxidation process to form a stable protective film, and the reliability can be improved.

Further, both the selective oxidation layer and the AlGaAs layer formed thereon are oxidized, and the oxidation surface of the selective oxidation layer is closer to the oxidation progressing direction than the oxidation surface at the interface between the selective oxidation layer and the AlGaAs layer. It is also possible that there is a step between both oxidation surfaces. That is, both the selective oxidation layer itself and the AlGaAs layer formed thereon are oxidized, the stress of the selective oxidation layer is relieved, the effective refractive index difference is increased, and the effect of the actual refractive index guide is increased. be able to.
This also leads to an increase in the thickness of the constriction layer and an increase in resistance to leaks. In particular, the oxidation surface of the selective oxidation layer is more advanced than the oxidation surface at the interface in the oxidation progressing direction, a step is generated between the upper and lower interfaces, and the current confinement section has a funnel-shaped cross section, so that the current flow is increased. It is possible to gradually concentrate on the narrowed portion and improve the leak resistance.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention utilizes a simple process of steam oxidation to selectively oxidize a semiconductor layer containing Al to realize a unique current confinement structure, high performance and long life. The light emitting element of is manufactured with good reproducibility.

First, as a technique related to the present invention, a manufacturing process of a semiconductor light emitting device using a steam oxidation process will be described. FIG. 6 is a schematic cross-sectional structure of a light emitting device obtained using a steam oxidation process. That is, the illustrated light emitting device is an LD having a block layer in which AlGaAs is selectively oxidized. In manufacturing this LD, first, an n-type I is formed on a semiconductor substrate 121 such as n-type GaAs.
nGaAlP lower clad layer 122, active layer 123 such as InGaAlP, p-type InGaAlP intermediate clad layer 1
24, AlGaAs oxidized layer 125, p-type InGaAl
The P upper clad layer 126 and the GaAs cap layer 127 are laminated. Here, each clad layer 122, 124, 12
In No. 6, the composition is adjusted so that the band gap becomes larger than that of the active layer 123.

Next, the growth layer is mesa-etched to form AlG.
The end of the aAs oxidized layer 125 is exposed, and heat treatment is performed at 400 to 500 ° C. in a steam atmosphere. After that, the electrode 128 is formed.

AlGaAs is oxidized by heat treatment in water vapor and converted into Al ₂ O ₃ and becomes an insulator. However, its oxidation rate changes significantly depending on the Al composition. Therefore, for example, by setting x and y above x <y and y = 0.9 to 1, the cladding layer and the GaAs layer are hardly affected. Only the oxidized layer 125 can be selectively oxidized. By appropriately adjusting the temperature and time of heat treatment,
Opening 12 where a part of the AlGaAs oxidized layer is not oxidized
It remains as 9, and electric current constriction can be performed. A current is injected only into the active layer immediately below the opening 129 to have a gain and become the active region 130.

Further, since the semiconductors such as the active layer and the cladding layer have a refractive index of 3.0 to 3.5, the refractive index of oxidized Al ₂ O ₃ is lowered to about 1.5. Also, the equivalent refractive index in areas other than the active region is lowered, and light can be confined in the active region 129. In addition, wavelength 650nm
In the case of a red light laser such as
Alternatively, the upper and lower clad layers 122, 124, and 125 may be made of aP and made of InGaAlP.

By utilizing steam oxidation, it is possible to manufacture an LD operating at a low current in such a simple process.
Some problems remain. That is, when AlAs or AlGaAs is steam-oxidized, there is a problem that the volume of the layer to be oxidized contracts and strain is applied to the upper and lower layers. In order to carry out current narrowing effectively, the oxidizable layer that becomes the block layer needs to have a certain thickness, but the thicker this layer, the greater the strain. Then, the strain concentrates on the tip of the oxide layer, but since the layer to be oxidized 125 is provided at a short distance of 0.2 μm from the active layer 123, this strain affects the region of the active layer where the current is most concentrated, This will shorten the life of the device.

On the other hand, in order to extend the life, the active layer 123
Although it is desirable to avoid exposing the ends of the layer to the air as much as possible, in order to perform steam oxidation, the layer to be oxidized 125
The end of the must be exposed. However, it is difficult to perform this etching with good controllability because the layer to be oxidized is provided in the closest distance to the active layer.

Furthermore, AlAs or A having a high Al composition
lGaAs has a large band gap, and the cladding layer 12
The injection of carriers is apt to be hindered by the difference in band gap from No. 6. This means that heat is generated by the resistance component, and there is also a problem that the life is shortened.

Further, in the case of the LD of 650 nm band, since the selective oxidation layer is sandwiched by the high resistance quaternary (InGaAlP) layers, it is difficult to reduce the element resistance and the mesa formation process is complicated. Furthermore, the quaternary layer also has a very low thermal resistance and the temperature characteristics of the light emitting element are not sufficient. Further, the selective oxidation process is accompanied by stress, which is a negative factor in reliability.

In consideration of the above circumstances, the present inventor has further improved the structure of the light emitting element using the selective oxidation technique and has invented a unique structure. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view illustrating a light emitting device according to the first embodiment of the present invention. The light emitting element in the figure is an InAlGaP based semiconductor laser, and its configuration will be described below along with the manufacturing process. First, on the n-type GaAs substrate 11, for example, n-type InGa
A lower clad layer 12 made of AlP and having a thickness of 1.1 μm,
0.17 μm thick active layer 13, 0.2 μm thick intermediate clad layer 14 made of p-type InGaAlP, Al _X G
a _1-X As made of 0.1 μm thick passivation layer 1
5, a selective oxidation layer 16 made of Al _Y Ga _{1 -Y} As and having a thickness of 500 Å, an upper cladding layer 17 made of InGaAlP and having a thickness of 0.9 μm, an easy conduction layer 18 made of InGaP and having a thickness of 500 Å, and GaA
500 angstrom thick cap layer 1 of s
9 are sequentially laminated. Here, the composition ratios X and Y are 0.7 ≦
It is desirable to satisfy the relationship of X <Y ≦ 1, and X = 0.
9, and it is more desirable to set Y = 1.

The active layer 13 is, for example, an InGaAlP barrier layer having a thickness of 35 Å and a thickness of 40.
Multiple quantum well structure in which a plurality of AngGa InGaP well layers are alternately stacked.
MQW).

Next, in this laminated structure, each layer above the selective oxidation layer 16 is processed into a mesa shape by a photolithography process as illustrated. Specifically, after removing only the GaAs cap layer 19 with a sulfuric acid-based etchant, a hydrochloric acid-based etchant is used to leave the AlGaAs passivation layer 15 having a low Al composition and leave InGa.
The P-conduction easy layer 18, the InGaAlP clad layer 17, and the AlGaAs selective oxidation layer 16 having a high Al composition can be selectively removed. The formation of the electrode 20 may be performed before or after the steam oxidation described below.

The wafer thus formed with mesas is heat-treated at 400 ° C. for 10 minutes in a water vapor atmosphere. Then, the AlGaAs passivation layer 15
In the AlGaAs selective oxidation layer 16, the oxidation proceeds in the depth direction from the surface, and the oxidation proceeds in the lateral direction from the exposed end surface of the mesa to form an Al oxide layer. Selective oxide layer 16
Since the Al composition may be higher than that of the passivation layer 15, the oxidation rate in the lateral direction, that is, the direction parallel to the major surface of the layer is overwhelmingly high. However, oxygen or water vapor that has penetrated into the selective oxidation layer 16 diffuses into the passivate layer 15 and oxidizes, so that the cross-sectional shape of the finally obtained oxide layer is as shown by the symbol B in FIG. It becomes wedge-shaped. The wedge-shaped oxide layer B acts as a current blocking region.

That is, the oxide layer P formed near the surface of the passivate layer 15 exposed along the bottom surface of the mesa.
Has a constant thickness, and at the end of the mesa, the oxide layer of the selective oxidation layer 16 is also added to increase the film thickness of the current block region B, which gradually becomes thinner toward the inside of the mesa and extends like a wedge. . Therefore, the distortion due to volume contraction is small in the tip portion 302 of the oxide film and is relaxed in the lateral direction, so that the influence on the active layer 13 is small and the life of the element is extended.

In addition, the current block area B at the end of the mesa
Has a sufficient thickness, it becomes a more effective current confinement layer than the single layer to be oxidized as shown in FIG. 6, and the optical confinement effect is also high.

Moreover, the oxide layer 303 on the surface of the passivation layer 15 obtained by steam oxidation functions as a good passivation film. Further, by using AlGaAs having different compositions for the current narrowing layer 16 and the passivation layer 15, the band gap difference at the hetero interface is relaxed,
Suppresses heat generation due to the resistance component. These effects are also effective in extending the life of the device.

In the above example, the case where the selective oxidation step is performed on the wafer on which the mesa is formed has been described. However, in addition to this, for example, the LD is formed by cleavage.
Alternatively, the chips may be separated and then selectively oxidized. By doing so, the selective oxidation layer exposed on the end face of the LD is also oxidized, and the current block layer can be formed along the end face. That is, it is possible to form a so-called "window structure" in which no current is injected into the end face. This can prevent optical damage on the end face, which also contributes to prolonging the life of the device. The selective oxidation layer 16 and the upper cladding layer 1
An Al _z Ga _1-z As layer satisfying Z <Y may be further inserted between 7 and 7.

Next, a second embodiment of the present invention will be described. FIG. 2 is a sectional view showing a schematic structure of a semiconductor light emitting device according to the second embodiment of the present invention. That is, the semiconductor light emitting device in the figure is an InGaAlP-based light emitting diode (LED). In the figure, 30 is n-type GaAs
It is a substrate, and 10 cycles of InAl are formed on the substrate 30.
DBR (distributed Braggrefle) made of P / GaAs
ctor: Distributed Bragg reflector) 31, 1 μm thick n-type I
nGaAlP clad layer 32, total thickness 0.5 μm
InGaP / InGaAlP strained quantum well active layer 3
3 and a p-type InGaAlP clad layer 3 having a thickness of 1 μm
4 is formed, and a p-type AlGaAs selective oxidation layer 35 having a thickness of 0.05 μm and a p-type A having a thickness of 1 μm are formed on the upper part of the layer 4.
An lGaAs layer 36 is formed, and a p-type GaAs contact layer 37 having a thickness of 0.2 μm is formed by circularly opening the light extraction portion. A p-side circular electrode 38 is formed on the p-type contact layer, and an n-side electrode 39 is formed on the back surface of the substrate. The LED in the figure emits light from the opening on the p side, as indicated by the arrow in the figure. Therefore, the Al composition ratio x of the AlGaAs layer 36 needs to have a small absorption effect with respect to the emission wavelength, and is preferably 0.7 or more.

The illustrated mesa structure can be formed by a single etching process by using a selective etch of InGaAlP and AlGaAs, for example, SH etchant. Further, heat treatment is performed in a steam atmosphere to oxidize the AlGaAs selective oxidation layer 35 from the side surface of the mesa to form the current block region B.
The AlGaAs selective oxidation layer 35 needs to have a composition that is more easily oxidized than the AlGaAs layer 36. Therefore, the Al composition of the AlGaAs selective oxidation layer 35 is preferably set higher than that of the AlGaAs layer 36, and may be composed of AlAs not containing Ga.

In this embodiment, in the InGaAlP-based light emitting device, the AlGaAs layer 36 is provided on the selective oxidation layer 35.
One of the features is the point.

By providing the AlGaAs layer 36 on the AlGaAs selective oxidation layer 35 for current confinement in this way, the operating current of the device can be lowered and the temperature characteristics can be further improved. The reason is that AlGaAs has
This is because it has lower electric resistance and thermal resistance than nGaAlP. That is, when the InGaAlP layer is laminated on the selective oxidation layer as in the structure shown in FIG. 6, the electric resistance of the current path concentrated in the current constriction portion is high, and the heat dissipation is not sufficient. There's a problem. On the other hand, according to the present embodiment, by providing the AlGaAs layer 36, the electrical resistance of the current path concentrated in the current constriction portion is reduced, and the heat generated in the active layer 33 is efficiently diffused to emit light. The thermal characteristics of the device can be improved.

That is, according to this embodiment, it is possible to realize an LED having a simple manufacturing process and a high current confinement effect and a high heat dissipation effect. The same effect can be obtained by directly applying the basic structure of the present embodiment to the LD.

Next, a third embodiment of the present invention will be described. FIG. 3 is a schematic sectional view illustrating a semiconductor light emitting device according to the third embodiment of the present invention. That is,
The light emitting element in the figure is an InGaAlP-based LD. In the figure, reference numeral 50 denotes an n-type GaAs substrate, and on this substrate 50, an n-type InGaAlP clad layer 5 having a thickness of 1.1 μm.
2. InGaP / InGaA with a total thickness of 0.1 μm
1P strained quantum well active layer 53, 0.2 μm thick p-type I
An nGaAlP cladding layer 54 is formed, and a p-type AlAs selective oxidation layer 5 having a thickness of 0.05 μm is formed on the nGaAlP cladding layer 54.
5, p-type AlGaAs layer 56 having a thickness of 1 μm, thickness of 0.2
A μ-type p-type GaAs contact layer 57 is formed, and a p-side electrode 58 is formed on the p-type contact layer and an n-side electrode 59 is formed on the back surface of the substrate. Mesa width L in the figure
Can be, for example, about 10 μm so as to follow high-speed modulation.

The illustrated mesa structure can be formed by a single etching process by using InGaAlP-based and AlGaAs-based selective etching, for example, SH etchant. Further, by performing heat treatment in a steam atmosphere, the AlGaAs selective oxidation layer 55 is oxidized from the side surface of the mesa to form the current block region B.
The AlGaAs selective oxidation layer 55 needs to have a composition that is more easily oxidized than the AlGaAs layer 56. Therefore, the Al composition of the AlGaAs selective oxidation layer 55 is preferably set higher than that of the AlGaAs layer 56, and may be composed of AlAs that does not contain Ga.

Also in the present embodiment, by providing the AlGaAs layer 56 on the selective oxidation layer 55, it is possible to obtain the same effect of reducing the element resistance and improving the temperature characteristics as described above with reference to FIG.

Further, the present embodiment is also characterized in that the side surface of the AlGaAs layer 56 is also oxidized in the oxidation treatment of the selective oxidation layer 55 to form the oxide layer P. The oxide layer P acts as a passivation film, that is, a protective film for the AlGaAs layer 56. That is, Al
It is desirable that the GaAs layer 56 has a large Al composition ratio in order to reduce absorption of light emitted from the active layer 53. On the other hand, if the Al composition ratio is increased, the GaAs layer 56 is likely to be oxidized and the characteristics of the light emitting element are improved with time. There is a problem of deterioration and deterioration of reliability. On the other hand, according to the present embodiment, by forming the oxide layer P on the side surface of the AlGaAs layer 56, the surface can be stabilized and the progress of oxidation of the AlGaAs layer 56 can be suppressed. As a result, stable operation can be performed over a long period of time.

Next, a fourth embodiment of the present invention will be described. FIG. 4A is a schematic sectional view showing a semiconductor light emitting device according to a fourth embodiment of the present invention, and FIG. 4B is a partially enlarged view thereof. That is, the light emitting device in the figure is an InGaAlP-based LD. In the figure, reference numeral 60 denotes an n-type GaAs substrate. On this substrate 60, an n-type InGaAlP clad layer 62 having a thickness of 1.1 μm, an InGaP / InGaAlP strained quantum well active layer 63 having a total thickness of 0.1 μm, and a thickness of 0.2 μm p-type InG
An aAlP clad layer 64 is formed, and a p-type AlAs selective oxidation layer 65 having a thickness of 0.05 μm, a p-type AlGaAs quasi-oxidation layer 66 having a thickness of 0.1 μm, and a thickness of 1 are formed on the aAlP clad layer 64.
A μm p-type AlGaAs layer 67 and a 0.2 μm-thick p-type GaAs contact layer 68 are formed, and a p-side electrode 69 is formed on the upper part of the p-type contact layer and an n-side electrode 70 is formed on the back surface of the substrate. ing. AlGaAs quasi oxide layer 66
Has an Al composition intermediate between the AlAs selective oxidation layer 65 and the AlGaAs layer 67. For example, the Al composition ratio is 0.9 or more and less than 1.

The illustrated mesa structure can be formed by one etching process by using InGaAlP-based and AlGaAs-based selective etching, for example, SH etchant. Further, heat treatment is performed in a water vapor atmosphere to oxidize the AlAs selective oxidation layer 65 from the side surface of the mesa to form the current block region B. The quasi-oxidized layer 66 is also oxidized during this oxidation treatment, but its oxidation rate is slower than that of the selective oxidation layer 65, and the oxidation proceeds mainly from the interface with the selective oxidation layer.

As described above with reference to FIG. 3, Al
The side surface of the GaAs layer 67 is also oxidized to form an oxide layer P that acts as a protective film. Further, the InAlP clad layer 64 is also oxidized by the same process, but the oxidation rate thereof is also orders of magnitude slower than that of AlAs, and only the surface is oxidized to form the oxide layer P ′. This surface oxide layer P '
Also functions as a protective film.

As described above, according to this embodiment, in addition to the effects of the above-described second and third embodiments, the oxidation region of the selective oxidation layer is located in the direction of progress of oxidation rather than the oxidation surface at the interface. It is moving forward, creating a step between each layer,
The current constriction portion B has a funnel-shaped cross section. As a result, as described above with reference to FIG. 1, it is possible to reduce the adverse effect of strain caused by the oxide film. Furthermore, the injection current can be gradually concentrated in the narrowed portion, and the leak resistance can be improved. In addition, the thickness of the oxidized portion B can be increased with almost no change in the oxidation progress rate of the AlAs selective oxidation layer 65, and the current blocking effect and the leak resistance can be improved without changing the conditions. .

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples, and various modifications can be carried out without departing from the gist of the present invention. For example, in the above-described specific examples, the InGaAlP-based semiconductor light emitting device is provided with the AlGaAs-based oxidizable layer.
In addition, for example, as the layer to be oxidized, AlGaP, Al
Any compound containing Al such as InAs, AlInP, AlSb, and AlN can be used. In addition, as a layer that is not oxidized such as a clad layer, GaAs, In
P, InGaAsP, InGaSb, InGaN, etc., A
Any compound that does not contain 1 or has a low Al concentration can be used.

Further, in the above-mentioned specific example, the layers to be oxidized are two AlGaAs layers having different Al compositions, but the same effect can be obtained even if the layers are three layers or more, so-called gray in which the Al composition is gradually changed. A dead layer can also be used.

Further, although the examples applied mainly to the edge emitting LD have been explained so far, the surface emitting LD and L are used.
It goes without saying that it can be applied to ED. At this time,
As the DBR serving as a reflector, other than InAlAs / GaAs described in the second embodiment, for example, AlAs / Ga
It is also possible to stack with an As semiconductor layer, and to form MgF / ZnSe, SiO ₂ / TiO ₂ , Si / S on the surface of the semiconductor layer.
It is also possible to stack thin films of iO ₂ , MgO / Si, CaF ₂ / Si, or the like.

In addition to the semiconductor light emitting device such as the semiconductor laser and the light emitting diode, the present invention also provides a photodiode, a transistor, and a FET (feild effect transistor).
r), HEMT (high electron mobility transistor)
Etc., it is possible to obtain various effects.

[0058]

According to the present invention, the selective oxidation layer itself and the Al-containing layer formed adjacent to the selective oxidation layer are both oxidized, so that the stress of the selective oxidation portion serving as the current block region is reduced. The effect of the actual refractive index guide can be enhanced by alleviating and further increasing the effective refractive index difference.

This also leads to an increase in the thickness of the constriction layer and an improvement in resistance to leakage. In particular,
The oxidation surface of the selective oxidation layer is advanced in the direction of progress of oxidation relative to the oxidation surface at the interface, and a step is created between both interfaces to make the cross section of the current constriction portion funnel-shaped so that the current is constricted. The leak resistance can be improved while gradually being concentrated.

Further, according to the present invention, in particular, InGaA
In the 1P-based light emitting device, the device resistance can be reduced and efficient carrier injection can be achieved by forming a current injection part made of AlGaAs on the selective oxidation layer containing AlAs, which can easily obtain a resistance lower than quaternary. it can.

Furthermore, InGaAlP and AlGaAs
The selective etching of the system makes it possible to form the mesas in a single process and reduce the cost.

Further, in the case of the narrow mesa structure, not only the selective oxidation layer but also the side surfaces of the mesa are oxidized by the selective oxidation process to form a stable protective film, and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating a light emitting device according to a first embodiment of the invention.

FIG. 2 is a sectional view showing a schematic structure of a semiconductor light emitting device according to a second embodiment of the invention.

FIG. 3 is a schematic cross-sectional view illustrating a semiconductor light emitting device according to a third embodiment of the present invention.

FIG. 4A is a schematic cross-sectional view showing a semiconductor light emitting device according to a fourth embodiment of the present invention, and FIG.
Is a partially enlarged view of FIG.

FIG. 5 is a schematic cross-sectional view showing a configuration of a main part of a conventional LD.

FIG. 6 is a schematic cross-sectional structure of a light emitting device obtained by using a steam oxidation process.

[Explanation of symbols]

11 n-type GaAs substrate 12 lower clad layer 13 active layer 14 intermediate clad layer 15 passivate layer 16 selective oxidation layer 17 upper clad layer 18 conductive layer 19 cap layer 30 n-type GaAs substrate 31 DBR (distributed Bragg reflector) ) 32 n-type InGaAlP clad layer 32 33 InGaP / InGaAlP strained quantum well active layer 34 p-type InGaAlP clad layer 35 p-type AlGaAs selective oxide layer 36 p-type AlGaAs layer 37 p-type GaAs contact layer 38 p-side circular electrode 39 n-side electrode 50 n-type GaAs substrate 52 n-type InGaAlP clad layer 53 InGaP / InGaAlP strained quantum well active layer 53 54 p-type InGaAlP clad layer 55 p-type AlAs selective oxidation layer 56 p-type AlGaAs layer 57 p-type GaAs contour Layer 58 p-side electrode 59 n-side electrode 60 n-type GaAs substrate 62 n-type InGaAlP clad layer 63 InGaP / InGaAlP strained quantum well active layer 64 p-type InGaAlP clad layer 65 p-type AlAs selective oxidation layer 66 p-type AlGaAs quasi-oxidation layer 67 p-type AlGaAs layer 68 p-type GaAs contact layer 69 p-side electrode 69 70 n-side electrode 101 substrate 102 lower clad layer 103 active layer 104 upper clad layer 105 block layer 106 p-type contact layer 107 p-side electrode 108 n-side electrode 121 n-type GaAs substrate 122 n-type InGaAlP lower clad layer 123 active layer 124 p-type InGaAlP intermediate clad layer 125 AlGaAs oxidized layer 126 p-type InGaAlP upper clad layer 127 GaAs cap layer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-9-74219 (JP, A) JP-A-10-4239 (JP, A) JP-A-51-140586 (JP, A) JP-A-10- 22569 (JP, A) JP 53-113472 (JP, A) JP 9-167877 (JP, A) JP 10-125999 (JP, A) JP 9-36345 (JP, A) JP-A-7-263747 (JP, A) JP-A-10-135564 (JP, A) JP-A-10-223981 (JP, A) JP-A-9-27650 (JP, A) JP-A-11-68231 (JP, A) Tokumei Hyo 6-503919 (JP, A) Tokumei Hyo 9-511872 (JP, A) International Publication 99/008351 (WO, A1) Electronics Letters, 1997, 33 [4], p. ． 300-301 Electronics Letters, 1997, 33 [10], p. 869-871 Electronics Letters, 1996, 32 [2], p. 114-116 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 33/00 H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. An active layer, a first layer provided on the active layer and containing aluminum, and laminated on the first layer so as to form a mesa, and more than the first layer. A second layer containing a high concentration of aluminum, wherein the first layer exposed on the bottom surface of the mesa and the second layer exposed on the side surface of the mesa are respectively oxidized,
A semiconductor light emitting device having an oxide region having a wedge-shaped cross-section, the thickness of which decreases toward the inside of the mesa. 2. A step of laminating an active layer on a semiconductor substrate, a step of laminating a first semiconductor layer containing aluminum on the active layer, and a step of laminating aluminum on the first semiconductor layer. Second
Stacking the semiconductor layers, partially removing the first semiconductor layer by removing the second semiconductor layer to form a mesa, and raising the temperature in a water vapor atmosphere. And a step of oxidizing the first semiconductor layer exposed on the bottom surface of the mesa and the side surface of the second semiconductor layer exposed on the side surface of the mesa, respectively. Production method.