JPH0260077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor light emitting device, particularly a semiconductor laser device.

(Conventional technology) Conventionally, as a light emitting element in this field,
AlGaAs semiconductor laser devices are known. this
In AlGaAs semiconductor laser devices, an internal current confinement channel stripe structure is said to be effective in realizing low threshold oscillation and transverse fundamental mode oscillation.

A method of manufacturing such a conventional AlGaAs semiconductor laser device will be briefly explained with reference to manufacturing process diagrams shown in FIGS. 2A to 2C.

First, a p-GaAs substrate 20 is prepared, and an n-GaAs layer 21 that can serve as a current blocking layer (also referred to as a current confinement layer) is crystal-grown on the substrate surface 20a by liquid phase epitaxial growth or other method. Figure A]. Subsequently, as shown in FIG. 2B, a striped V-groove 22 is formed with a depth that reaches the substrate 20 by a normal photolithography and etching process.

Next, this V-groove 22 portion and the remaining n-
A second crystal growth is performed on the GaAs layer 21 by liquid phase epitaxial growth to form a p-AlGaAs layer 23 as a first cladding layer and a p-AlGaAs layer 23 as an active layer.
AlGaAs24, n- as second cladding layer
AlGaAs layer 25, n- as a contact layer
A GaAs layer 26 is grown in sequence, and then an n-side electrode 27 and a p-side electrode 28 are deposited on the upper and lower surfaces by vapor deposition to obtain a structure as shown in FIG. 2C.

In the structure of such a semiconductor laser device,
The current injected from the p-side electrode 28 flows through the substrate 20 → the portion 23a of the first cladding layer 23 → the active layer 24 → the second cladding layer 25 → the contact layer 26 → the n-side electrode 27 and the current confinement portion 30. Since the boundary between the current blocking layer 21 and the first cladding layer 23 is reverse biased from n to p, current flows through the p-side electrode 28 → substrate 20 → current blocking layer 21 → first cladding layer 23. I can't. Therefore, since only the current path passing through the current confinement portion 30 is selected, the region portion 2 of the active layer 24 above the V-groove 22
Current is effectively concentrated in 4a (light emitting region), allowing low threshold current oscillation. Furthermore, the thickness of the flat portion 23b of the first cladding layer 23 is insufficient to confine light, and the light from the light emitting region 24a is confined only to the portion 23a of the first cladding layer 23 having a sufficient thickness. Therefore, it is configured to oscillate in the transverse fundamental mode.

(Problems to be Solved by the Invention) However, in the conventional manufacturing method, during the second liquid phase epitaxial growth, crystal growth is performed on a substrate with unevenness (V-groove 22). It was difficult to control the thickness. In other words, since the crystal growth rate inside the trench is different from that outside the trench, the AlGaAs layer 2 as the first cladding layer
3, the surface of the portion 23a filling the inside of the V-groove 22 is made flat, and the film thickness of the flat portion 23b outside the V-groove 22 is set to a thickness that does not have a light trapping function ( It is difficult to suppress the thickness to 0.2 to 0.4 μm), and the thickness of the flat portion shown by 23b becomes thick, which makes it impossible to secure the transverse fundamental mode sufficiently, resulting in the disadvantage that good characteristics cannot be obtained.

Furthermore, during the growth of the first cladding layer 23, the shoulder portion 29 of the V-groove 22 is likely to be melted back, so the entrance portion of the V-groove 22 tends to become wider than its initial width. It was difficult to stabilize the transverse fundamental mode. Thus, with conventional manufacturing methods, it has been difficult to create a structure that achieves a predetermined performance.

An object of the present invention is to provide a light-emitting device in which the thickness of a crystal-grown layer can be accurately and easily controlled, and a current path can be formed with good reproducibility without causing a current narrowing width, that is, a widening of the oscillation part. The purpose of this invention is to provide a method for manufacturing the same.

(Means for Solving the Problem) In order to achieve this object, according to the method of the present invention, a first clad layer of AlGaAs, an active layer of AlGaAs, and an active layer of AlGaAs are formed to form a double heterojunction on a semiconductor substrate of GaAs. a first step of sequentially growing a second cladding layer and a first layer of GaAs for current blocking on the second cladding layer; a second step of etching to form a thin layer and a thick protrusion, and a second layer of AlGaAs for current blocking on the etched surface of the first layer excluding the top surface of the protrusion. a third step of growing a portion of the second cladding layer corresponding to the lower side of the protrusion by utilizing the difference in meltback speed during liquid phase epitaxial growth in the first layer and the second layer; a fourth step of forming a groove that reaches the second layer, and then forming a groove in the groove and on the remaining second layer;
A fifth step in which a third cladding layer of AlGaAs and a contact layer of GaAs are sequentially grown by liquid phase epitaxial growth.
The method is characterized in that the third step, the fourth step, and the fifth step are performed continuously in the same growth reactor.

(Function) According to such a configuration, after crystal growth of the double heterostructure, meltback of the crystal growth is performed, and moreover, during crystal growth, the protrusion of the first layer for current blocking formed in advance is removed. Since the second layer for current blocking is grown only on the etched surface of the first layer below the top surface and then meltbacked, the thickness of the second cladding layer can be precisely controlled during the growth of the double heterostructure. In addition, since the second layer is not grown on the top surface of the protrusion of the first layer, the current confinement width can be controlled with good reproducibility. Therefore, an internal current confinement channel that oscillates in a stable transverse fundamental mode can be created. A light emitting element with a striped structure can be simply and easily manufactured.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1A to 1E.

1A to 1E are cross-sectional views schematically showing the state of the device at the main manufacturing stages to explain the manufacturing process of a GaAs semiconductor laser device as an example, and hatching etc. representing the cross section are omitted. . First of all,
As shown in FIG. 1A, an n-GaAs substrate 1 is prepared, and each layer forming a double heterojunction structure, that is, n-Al _y Ga ₁ as a first cladding layer, is prepared on the substrate surface 1a of the substrate 1. _-y As layer 2, p-Al _x Ga _1-x As layer 3 as an active layer, p-Al _y Ga _1-y As layer 4 as a second cladding layer, and current blocking on this second cladding layer 4. In the first crystal growth, the n-GaAs layer 5 as a first layer is grown one after another. The growth method in this case can be any suitable crystal growth method, such as liquid phase epitaxial growth, which allows accurate film thickness control. In this crystal growth, the thickness of the second cladding layer 4 is set to a thin layer that does not have an optical confinement function, for example, 0.2~
The thickness can be accurately and easily controlled to 0.4 μm.

Next, as shown in FIG. 1B, the first layer 5 is etched using a conventional photolithography and etching process.
A portion of the surface is etched and removed to form a striped inverted mesa structure protrusion 5a in the center. This etching is performed using a mask over a part of the thickness of the first layer 5, and the remaining part whose thickness has been reduced by etching is indicated by 5b. At this time, the width of the inverted mesa-shaped striped protrusion 5a is related to the current confinement effect and the stabilization of the transverse fundamental mode, so the width is set to 3 to 5 μm, and the height is set to 1.5 to 2 μm.
It is preferable that the thickness of the remaining portion 5b is 1 to 1.5 μm, and its control is accurate and easy.

Next, as shown in FIGS. 1C to 1E, a second crystal growth is performed on the first layer 5 on which the protrusion 5a is formed, and an n-
Grow an Al _z Ga _1-z As layer (X<Z), then
p-Al _y Ga _1-y As layer 7 as a third cladding layer;
The p-GaAs layer 8 as a contact layer is grown successively by liquid phase epitaxial growth in the same growth process, ie without any exposure of the growth reactor to the atmosphere.

During this second growth, first, as shown in FIG. 1C, n-Al _z which can serve as a current blocking layer is grown.
The Ga _1-z As layer 6 is heated to about 40°C at a melt supersaturation level of 3 to 4°C.
Grow for ~60 seconds to form. Under this condition, the Al _z Ga _1-z As layer 6 grows only on the etched surface 5c of the remaining portion 5b of the first layer 5, and does not grow on the upper surface 5d of the protrusion.

Next, in the same crystal growth process, the GaAs protrusion 5a and the surface of the Al _z Ga _1-z As second layer 6 are melt-backed using an unsaturated GaAs solution, as shown in FIG. 1D. , stripe-shaped grooves 9 are formed in this second layer 6 and the remaining portion 5b of the first layer 5. At this time, the meltback speed of GaAs is
Since the meltback speed is sufficiently higher than that of AlGaAs, the meltback progresses faster in the protrusion 5a than in the second layer 6. Therefore, only the protrusion 5a is selectively melt-etched, and finally, as shown in FIG. 1D, the protrusion 5a is completely removed and the surface of the second cladding layer 4 is exposed. The remaining portion 5b of the first layer and the portion of the second layer 6 remaining by this melt-etch form a current confinement layer (current blocking layer) 10, and a portion 11 of this groove 9 becomes a current confinement portion.

In this case, suitable melt-back conditions can be set depending on the material to be melt-backed, its thickness, and other requirements.

Next, as shown in FIG. 1E, a third cladding layer of p--
An Al _y Ga _1-y As layer 7 is grown. Generally, it is difficult to perform liquid phase epitaxial growth on an AlGaAs layer once exposed to air. However, according to the present invention, the current confinement layer 10 as well as the second cladding layer 4 can be formed without exposing AlGaAs, which is easily oxidized when exposed to the atmosphere and is less likely to melt back than GaAs, to the atmosphere.
It is possible to form a groove 9 exposing a part of the surface of. The reason is that after forming the thin part 5b and the thick protrusion part 5a in the first layer 5,
Formation of the second layer 6 in the same growth process, without exposing the growth reactor to the atmosphere even once during the process.
Formation of current confinement layer 10 and groove 9 by meltback, growth of third cladding layer 7 on current confinement layer 10 including this groove 9, and contact layer 8 above it.
This is because growth can be achieved continuously. In this way, when a melt bag is used, the AlGaAs layer can be grown immediately after the melt bag, so that the second cladding layer, such as the p-
It becomes possible to grow the p-AlGaAs layer 7 on the AlGaAs layer 4 by liquid phase epitaxial growth. Incidentally, since the third cladding layer 7 and the second cladding layer 4 have the same composition, they become one by this crystal growth and act as the upper cladding layer 12 for the active layer 3. This growth causes the upper cladding layer 1
The thickness of the channel portion 12a of No. 2 can be made sufficiently thick to confine light. Subsequently, p
After attaching the side electrode 13 and the n-side electrode 14,
The structure of the semiconductor laser device shown in FIG.

By the way, when performing the above-mentioned meltback,
A method has also been proposed in which the second layer 6 is grown so as to completely bury the protrusion 5a and then melted back (Japanese Patent Application No. 87181/1982). however,
Since the meltback amount of AlGaAs is not constant with respect to the meltback time and has poor reproducibility, the protrusion 5a
If AlGaAs is also grown on the upper surface 5d of
Since AlGaAs also has to be melt-etched, it becomes impossible to form a current confinement width and a current path with good reproducibility. Therefore, in the present invention, the second layer 6 is controlled so as not to grow on the upper surface 5d of the protrusion 5a, so that only GaAs needs to be melt-etched, thereby making it possible to form a current path with good reproducibility. ing.

In this case, the first layer 5 may be formed of a material that has a current confinement effect, but it is not necessarily necessary, and any material that melts back is sufficient, and furthermore, it may have light absorption properties. It is suitable if

In the laser device having the structure shown in FIG. 1E obtained by the above-described method of the present invention, p
The current injected from the side electrode 13 flows through the contact layer 8.
→ Channel part 12a of upper cladding layer 12 → Active layer 3 → First cladding layer 2 → Substrate 1 → N-side electrode 14
However, since the current confinement layer 10 and the second cladding layer 4 below it are reversely biased, no current path is formed through the current confinement layer 10. Therefore, only the current path passing through the current confinement portion 11 is selected, and therefore the current is efficiently concentrated only in the current path portion (light emitting region) 3a of the active layer 3, allowing low threshold current oscillation. becomes.

Furthermore, since the thickness of the second cladding layer 4 is set to be insufficient for light confinement, the light emission in the light emitting region 3a is confined only in the upper cladding layer 12a having a sufficient thickness, so that a stable transverse fundamental mode can be achieved. can oscillate.

The invention is not limited to the embodiments described above. For example, in the embodiment described above, n-
Although a GaAs substrate is used, a p-GaAs substrate may also be used, in which case the conductivity types of the other layers may be changed accordingly. Current blocking layer 6 of n-Al _z Ga _1-z As
Since the Al composition ratio z of the active layer is larger than the composition ratio x of the active layer, the current blocking layer functions normally without causing optical switching even if an n-type or p-type substrate is used.

Furthermore, although the above-mentioned embodiments have been described with reference to semiconductor laser devices, the present invention is not limited thereto and can be applied to a wide variety of light emitting devices.

Further, the cross-sectional shape of the above-mentioned protrusion is not limited to the inverted mesa shape, but may be rectangular or triangular.

Furthermore, the manufacturing conditions for the above-mentioned element can be appropriately selected according to requirements.

Furthermore, the dimensions, shapes, and arrangement relationships of each part can be appropriately selected.

(Effects of the Invention) As is clear from the above description, according to the method for manufacturing a light emitting device of the present invention, a first cladding layer forming a double heterojunction on a flat substrate surface;
Since the active layer and the second cladding layer are grown in one crystal growth, for example, in the first liquid phase epitaxial growth, the thickness of each of these layers can be adjusted exactly as required.
Moreover, it is easily controllable, and because of this, the thickness of the second cladding layer can be accurately controlled, so that the transverse fundamental mode oscillation can be made more stable than in the conventional case.

Furthermore, according to the method of the present invention, the groove is formed using the difference in meltback speed of the materials used, and an internal current confinement layer is defined, so meltback does not occur at the shoulder portion of the V-groove as in the conventional method. First, it is possible to easily control the groove width as designed, thereby suppressing the spread of the oscillating portion, and stabilizing the transverse fundamental mode oscillation.

Furthermore, since the second layer for current blocking is not grown on the top surface of the protrusion of the first layer for current blocking during melt etching, the relationship between meltback time and current path formation can be controlled more easily than before. Therefore, a current path can be formed with good reproducibility.

Furthermore, since a melt bag is used during liquid phase epitaxial growth, it is possible to grow the third cladding layer of AlGaAs on the second cladding layer of AlGaAs, thus producing a high quality upper cladding layer. The oscillation characteristics can be improved.

As described above, according to the present invention, a light emitting device can be formed using selective melt etching that utilizes the dependence of meltback rate on Al composition ratio. Furthermore, since selective melt etching is used, AlGaAs can be used as the current blocking layer. moreover,
The reproducibility of channel formation is improved by not growing the second layer of AlGaAs for current blocking on the top surface of the protrusion of the first layer of GaAs for current blocking.

[Brief explanation of drawings]

1A to 1E are manufacturing process diagrams for explaining the method for manufacturing a light emitting device of the present invention, and FIGS. 2A to 2C are manufacturing process diagrams for explaining a conventional method for manufacturing a light emitting device. 1...Substrate (GaAs substrate), 1a... (of the substrate)
Surface, 2...first clad layer (Al _y Ga _1-y As layer),
3... Active layer (Al _x Ga _1-x As layer), 3a... Light emitting region, 4... Second cladding layer (Al _y Ga _1-y As layer), 5
...First layer (GaAs layer) (for current blocking), 5a
...Protrusion (of the first layer), 5b... (of the first layer)
Remaining part, 5c...Etched surface, 5d...Top surface of protrusion, 6...Second layer (of current blocking layer) (Al _z Ga _1-z
(As layer), 7...Third cladding layer, 8...Contact layer, 9...Striped groove, 10...Current confinement layer, 11...Current confinement portion, 12...Upper cladding layer, 12a... Channel portion, 13... p-side electrode, 14... n-side electrode.

Claims (1)

[Claims] 1. A first cladding layer of AlGaAs, an active layer of AlGaAs, a second cladding layer of AlGaAs forming a double heterojunction on a GaAs semiconductor substrate, and a current blocking layer on the second cladding layer. , a first layer of GaAs, and etching the first layer partially from its surface over a portion of its thickness to form a thinner layer and a thicker protrusion. a third step of growing a second layer of AlGaAs for current blocking on the etched surface of the first layer excluding the top surface of the protrusion; a fourth step of forming a groove reaching a portion of the second cladding layer corresponding to the lower side of the protrusion by utilizing the difference in meltback speed during liquid phase epitaxial growth; within and on the remaining second layer.
A fifth step in which a third cladding layer of AlGaAs and a contact layer of GaAs are sequentially grown by liquid phase epitaxial growth.
A method for manufacturing a light emitting device, comprising the steps of: performing the third step, the fourth step, and the fifth step continuously in the same growth reactor.