JPS62260380A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To remove abnormal growth and a crystal defect on the second growth start interface when a semiconductor laser is manufactured by using a crystal growth method having an unbalanced growth mechanism, such as an MOCVD method, an MBE method, etc., and to obtain the semiconductor laser, a transverse mode of which is stabilized and which has high reliability, by employing a liquid growth method for buried growth. CONSTITUTION:On a GaAs-GaAlAs group semiconductor laser, a buffer layer such as an N-GaAs buffer layer 2, a clad layer such as an N-Ga1-xAlx As clad layer 3, an active layer such as an undoped Ga1-yAlyAs active layer 4, a clad layer such as a P-Ga1-xAlxAs clad layer 5, a meltback layer such as a P-GaAs meltback layer 6, a layer such as a P-Ga1-x AlxAs layer 7 and a current constriction layer such as an N-GaAs current constriction layer 8 are formed onto a substrate such as an N-GaAs substrate 1 in succession. The current constriction layer 8 is removed selectively and a groove stripe is shaped, the P-GaAlAs layer 7 in a groove is removed, and the surface of the P-GaAs layer 6 is exposed. When liquid growth is conducted in a liquid growth furnace under the state, the P-GaAs layer 6 is melted back and melted into a liquid melt, and the P-GaAlAs layer 5 is exposed. A P-Ga1-xAlxAs layer 9 and a P-GaAs layer 10 are grown through a liquid growth method, and a P electrode 11 and an N electrode 12 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, and particularly relates to a semiconductor laser device using a metal organic chemical vapor deposition method (MOCVD method) or a single molecular beam epitaxy (MBE method).
This invention relates to a semiconductor laser fabricated using both a crystal growth method having a non-uniform growth mechanism such as the method (method) and a liquid phase growth method.

[Conventional technology]

In a semiconductor laser, a transverse mode control mechanism for stabilizing its internal oscillation mode is indispensable. In semiconductor lasers manufactured using liquid phase epitaxy, CSP (Channeled
(5) Ubstrate Planer However, when growth is performed on a similar grooved striped substrate using a crystal growth method that has a non-uniform growth mechanism such as the MOCVI method or MBE method, a unique growth mechanism that preserves the shape of the substrate and grows. Therefore, the active layer bends and bends.
An optical waveguide effect equivalent to that of a C8P laser cannot be expected, and
Crystal defects occur in the bent active layer portion, reducing reliability. Therefore, after growing evenly up to the active layer,
A structure in which a transverse mode control mechanism is provided in the grown layer above the active layer is considered, and an example thereof is shown in FIG.

This laser structure was described in Applied Physics Letter by J. J., Coleman et al.
sa 1980. Vol. 37.262.

[Problem that the invention seeks to solve]

The laser manufacturing method is to deposit n-GaAs on an n-GaAs substrate 1.
s buffer layer 2. n-GaAlAs cladding layer 3, active layer 4, p-GaAQAs cladding layer 5, nG
After the aAs current confinement layer 8 is sequentially grown by MOCVD, the upper current confinement layer 8 that performs laser emission and heating is removed by photolithography and chemical etching, and then P-
A GaA Q As cladding layer 9 and a p-GaAs cap layer 10 are grown by a progressive MOCVD method. Next, an n-electrode 12 and a p-electrode 11 are formed. In this structure, the current confinement layer 8 causes the current to flow concentrated in the light emitting region, and the fundamental transverse mode is realized by the light absorption of the current confinement layer 8.

However, this structure has a major drawback in its groove formation process. The conditions necessary for etching to form the grooves are that the current confinement layer 8 is completely removed and the etching is stopped as soon as the surface of the p-GaAlAS cladding layer 5 is exposed. For this purpose, a selective etching solution is suitable, in which the etching rate decreases as the molar ratio of Al increases.

An etching solution that satisfies this requirement is a mixed solution of ammonia solution and hydrogen peroxide. However, the reason why the etching rate becomes slower as the molar ratio of Al increases is explained by the fact that Al is oxidized and Ag2O3 is formed on the surface, which lowers the etching rate. When the second growth is performed on this oxide (A Q xis), the growth interface (p - G
There is a drawback that device characteristics deteriorate due to abnormal growth or introduction of crystal defects between the aA Q As layer 5 and the PGaA Q As 9.

Furthermore, since the groove is grown while preserving the groove stripe shape, concave portions remain on the element surface as shown in FIG. 2, resulting in poor dissipation of thermal energy generated inside the laser and a decrease in reliability.

An object of the present invention is to eliminate the above-mentioned drawbacks by utilizing a liquid phase growth method for buried growth of a semiconductor laser device manufactured using a crystal growth method having a non-uniform growth mechanism such as MOCVD method or MBE method. There is a particular thing.

[Means for solving problems]

As described above, conventional semiconductor lasers manufactured using the MOCVD method and the MBE method have problems such as bending of the active layer, abnormal growth during the second growth, or introduction of crystal defects.

Therefore, the present inventors considered using a liquid phase growth method in which growth is performed in a thermal equilibrium state for the second buried growth. At this time, a GaAs layer with almost no oxidation is formed at the growth interface inside the groove stripe, and immediately before the liquid phase growth in the liquid phase growth furnace, the GaAs is melted back and removed using the meltback characteristic of liquid phase growth. He invented the method of forming a buried growth layer immediately after that.

The present invention relates to such a laser structure.

The present invention will be explained in detail using FIG.

FIG. 1 shows an example of the present invention, GaAs-GaA Q A
This figure shows a cross-sectional structure of an s-based semiconductor laser. This structure includes an n-GaAs buffer layer 2, an n-Ga 1-xALxAs cladding layer 3, an n-GaAs buffer layer 2, an n-GaAs cladding layer 3,
Undoped Ga 1-yA1yAs active layer 4, p −
Gax-xAlxAs cladding layer 5, p-GaAs
Meltback layer 6, p-Ga r-xAlxAs layer 7
, the n-GaAsN current confinement layer 8 is sequentially provided, and the n-GaAs current constriction layer 8 in the portion corresponding to the light emitting stripe is selectively removed to form a trench stripe, and then the p-GaA Q in the trench stripe portion is selectively removed. As layer 7 is removed and p
- Expose the surface of the GaAs layer 6 (FIG. 1(a)). When liquid phase growth is performed in a liquid phase growth furnace in this state, the P-GaAs layer 6 melts back and melts into the liquid phase melt, and the p-GaAs layer 6 melts back into the liquid phase melt.
-GaA Q As layer 5 is exposed. At this time, Afl
Since the GaA n As layer containing p-GaA n As is difficult to null 1-back, the melt-back stops at the p-GaA n As p 5 surface. Then, p -G az-xAlxAs
After growing the layer 9 and p-GaAsJJ 10 by liquid phase growth, a p-electrode 11 and an n-electrode 12 are formed (FIG. 1(b)).

In the above, the molar ratio X of Al is 0.5. Y is 0.4
It is.

At this time, if the melt for growing the p-GaA Q As layer 9 is used in the liquid phase melt for melting back the p-GaAs layer 6, the buried growth interface (p-GaAlAs layer 5 and P
- the boundary of the GaA Q As layer 9) is not exposed to the air, so oxides are not formed and a good device can be stably obtained.

Furthermore, by burying the groove stripes by liquid phase growth, the element surface becomes flat as shown in Figure 1(b), and the present invention solves the heat dissipation problem that existed in conventional elements. can.

[Effect]

In the present invention, the buried growth interface is not exposed to air, so no oxide film is formed. This prevents the introduction of crystal defects into the buried interface or abnormal growth, so that the device characteristics of the laser do not deteriorate.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1, 3, and 4.

Embodiment 1 FIG. 1 is a sectional view of a laser device in which the present invention is applied to a GaA Q As semiconductor laser. As shown in FIG. 1, this structure consists of an n-G
aAs buffer layer (thickness 0.5 pm)2. n-Ga
1-xGaA1xAs cladding layer (thickness 1.5μm)
3. Undoped G a z-yA1yAs active layer (thickness 0.06 μm) 4 p -G a +-xAlxAs cladding layer (thickness 0.3 pm) 5. P GaAs meltback layer 6 (thickness 0.08 μm) p -G a 1-X
AIXAS layer 7 (thickness 0.03 μm), n-GaAs
Sequential MOCVD of ttt flow constriction layer 8 (thickness 0.6 μm)
Established by law. Here, X is Q, and 50.7 is 0.14. By photolithography on this wafer,
After forming a photoresist mask with a window width of 3 to 5 μm and using this mask as a mask, the n-GaAs layer 8 is selectively removed by reactive ion etching (CCQ zFx gas). As layer 7
is removed to expose the surface of the P GaAs layer 6 (FIG. 1(a)).

When liquid phase growth is performed in a long furnace with a liquid composition in this state, p-GaAsi 6 melts back and dissolves in the liquid phase melt, and the p-GaAlAs layer 5 is exposed. At this time, A
Since GaAlAsFF containing Q is difficult to melt back, meltback stops at the surface of the p-GaA Q As layer. Then p -G a 1-XA Q x
After growing the AsAs layer 9 and the GaAs layer 10 by liquid phase growth, a pg electrode 11 and an n electrode 12 are formed.
)).

The resonator length was cut to 300 um. Here X=0.5
It was set to 0. The above is the configuration of this embodiment, and the operation of this embodiment will be explained below.

In this example, an element that oscillated at a wavelength of 780 nm, a threshold current of 25 mA, and an optical output of 50 mvcv in the fundamental transverse mode could be obtained with good reproducibility. Furthermore, 2
Since abnormal growth and crystal defects are not generated at the interface where the second growth starts, reliability is improved, and a long life of 10,000 hours was obtained in an accelerated life test at 70° C. and a constant light output of 40 mW.

Example 2 FIG. 3 is a cross-sectional view of another embodiment of the invention.

The configuration and manufacturing procedure of this example are almost the same as those of Example 1, but anti-meltback n-Gao, soA Qo, and soAs layers (thickness: 500) are added to a part of the n-GaAs current confinement layer 8. is formed. That is, the n-GaAt flow constriction layer 8 of Example 1 has a three-layer structure, that is, Ga
As5 layer 8 +n -Gao, aA Q o, zAsA
1B12-GaAs layer 14, and the total thickness of the three layers is 0.
It was set to 8 μm.

This anti-meltback n-GaA Q As layer 13
The presence of the stripe suppresses meltback in areas other than the groove stripes, and reduces meltback in the side surfaces of the stripes that are particularly prone to meltback, improving controllability of the stripe width. 1
Almost the same characteristics were obtained.

Embodiment 3 FIG. 4 is a sectional view of another embodiment according to the present invention. The structure and manufacturing procedure of this example are almost the same as those of Example 1, but the difference is that the p-GaAs meltback layer 6 and p-GaA Q As layer 7 of Example 1 are not included. . That is, groove stripe etching is performed using non-selective wet etching (e.g. sulfuric acid-based etchant).
The etching is stopped in the middle of the n-GaAs layer 8 as shown in FIG.
After removing aAs, liquid phase growth is performed in the same manner as in Example 1.

Note that the present invention is not limited to the wavelength of around 0.78 μm shown in the examples, but also GaA Q As with a wavelength of 0.68 to 0.89 pm.
Similar results were obtained over the entire range of continuous oscillation at room temperature using a semiconductor laser device based on this method. The semiconductor laser device according to the present invention uses laser materials other than GaA Q As, such as I
The present invention can be similarly applied to nGaAsP-based and InGaP-based materials. Furthermore, the structure of the laser is not limited to one based on the 3WJ waveguide shown in each of the above embodiments, but may also include a LOG structure in which a light guide layer is provided adjacent to one side of the active layer, or a structure in which a light guide layer is provided adjacent to both sides of the active layer. SC to provide a light guide layer
GRIN-5CI ('vt
It can be similarly applied to structures etc. Furthermore, it is also effective for those in which the active layer has a quantum well structure, and it is also effective for structures in which the conductivity types are all reversed in each of the above embodiments (structures in which the conductivity types are reversed (pan, n is replaced with p)). The results were obtained.

〔Effect of the invention〕

According to the present invention, when manufacturing a semiconductor laser using a crystal growth method having a non-uniform growth mechanism such as the MOCVD method or MBE method, the second growth, which was a drawback of the conventional transverse mode control device, can be performed. Abnormal growth at the starting interface.

Since crystal defects can be removed, device characteristics are improved, particularly reliability.

As a result, we obtained a transverse fundamental mode with an optical output of 50 mW at a wavelength of 780 nm, and an average lifetime of optical output of 40 mtzcv.
It lasted for more than 10,000 hours at 70'C. Therefore, it has been revealed that the present invention is considerably effective in achieving transverse mode stabilization and highly reliable semiconductor lasers.

[Brief explanation of drawings]

FIGS. 1, 3, and 4 are cross-sectional views showing the configuration of an embodiment of a transverse mode controlled laser according to the present invention, and FIG. 2 is a cross-sectional view showing the configuration of a conventional transverse mode controlled laser. . 3-n-Gao, 6A QQ, 1lAs layer, 4
-Gao, ggA QQ, 14AS active layer, 5-
p-Gao, aAQo, sAs layer, 6-p-
GaAs meltback layer, 7-p-Gao, 5A
Q o, aAs layer, 8...n-GaAs layer, 9-p
-Gao, aA no, aAs layer.

Claims (1)

[Claims] 1. On the first semiconductor region of the first conductivity type, at least the first
a second semiconductor layer of a conductivity type, a third semiconductor layer having a larger refractive index and a smaller forbidden band width than the second semiconductor layer, a second conductive layer having a smaller refractive index and a larger forbidden band width than the third semiconductor layer; After sequentially providing a fourth semiconductor layer of the same type and a fifth semiconductor layer of the first conductivity type having a smaller forbidden band width than the third semiconductor layer, providing a trench stripe etched halfway into the fifth semiconductor layer; Next, the remainder of the fifth semiconductor layer within the groove stripe is completely removed by melt-back using a liquid phase growth method to expose the fourth semiconductor layer, and then the fourth semiconductor layer, which has a refractive index lower than that of the third semiconductor layer, is prohibited. A semiconductor laser device comprising a sixth semiconductor layer of a second conductivity type with a large band. 2. In the semiconductor laser device according to claim 1, after sequentially providing up to the fourth semiconductor layer, a seventh semiconductor layer having a narrower band gap than the third semiconductor layer; After providing an eighth semiconductor layer with a large forbidden band, and then providing the fifth semiconductor layer, the fifth semiconductor layer is etched using an etching method that makes it difficult to etch the eighth semiconductor layer. etching the semiconductor layer to provide a trench stripe in which the eighth semiconductor layer is exposed;
After etching the semiconductor layer to expose the seventh semiconductor layer, the seventh semiconductor layer is completely removed by melt-back using a liquid phase growth method to expose the fourth semiconductor layer, and then at least the seventh semiconductor layer is etched. 6. A semiconductor laser device characterized in that a semiconductor layer is provided by a liquid phase growth method. 3. In the semiconductor laser device according to any one of claims 1 to 2, a ninth semiconductor layer having a larger forbidden band width than the fifth semiconductor layer is provided in the middle of the fifth semiconductor layer. A semiconductor laser featuring: 4. In the semiconductor laser device according to any one of claims 1 to 3, the first to ninth semiconductor layers are Ga_1_-_xAl_xAs (0<x<1: x is A
Furthermore, the molar ratio of Al in the fifth and seventh semiconductor layers is 0.15 or less, and the molar ratio of Al in the eighth semiconductor layer is
A semiconductor laser device characterized in that the molar ratio of l is larger than the molar ratio of Al in the fifth and seventh semiconductor layers. 5. In the semiconductor laser device according to claim 1 or 4, the third semiconductor layer has a thickness of one or more layers.
A semiconductor laser device characterized in that it is formed from a quantum well layer with a thickness of Å to 300 Å. 6. A semiconductor laser device according to any one of claims 1 to 5, characterized in that it has two or more stripes for laser oscillation.