JP2708949B2 - Method of manufacturing semiconductor laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of manufacturing a buried stripe semiconductor laser device.

(Prior Art) Currently, semiconductor laser devices are widely used as light sources for consumer and industrial equipment for optical communication and information processing. For the characteristics (high power, high efficiency, high-speed modulation, etc.) required of these semiconductor laser devices, stabilization of the oscillation transverse mode and reduction of the oscillation threshold current are essential conditions. In particular, stabilization of the oscillation transverse mode is important because it has a close relationship with the fiber coupling efficiency for optical communication and the light beam astigmatism for information processing.

There have been many reports on the structure for controlling the oscillation transverse mode. In general, a semiconductor laser device having a Fabry-Perot resonator structure includes a gain waveguide type having a current confinement path, a built-in refractive index waveguide type having a refractive index distribution provided in a direction perpendicular to the resonator direction, and It is roughly classified into a refractive index waveguide type in which the waveguide side surface is embedded. FIG. 4 shows a buried stripe type semiconductor laser device as an example in consideration of stabilization of the oscillation transverse mode and reduction of the oscillation threshold current. This semiconductor laser device is manufactured as follows.

First, n-InP substrate 51 is formed by an appropriate crystal growth method.
-InP buffer layer 52, GaInAsP active layer 53, p-InP cladding layer 5
4, and a p-GaInAsP cap layer 55 are sequentially grown. Next, by photolithography and chemical etching, a stripe-shaped mesa portion (width 1 to 2) is formed in the resonator direction.
μm). Subsequently, the p-InP first current blocking layer 56 and the n-InP second current blocking layer 57 are sequentially grown again by an appropriate crystal growth method so as to bury the mesa portion. Finally, an n-side electrode 58 is placed on the back of the n-InP substrate 51, and pG
By forming a p-side electrode 59 on the surfaces of the aInAsP cap layer 55 and the n-InP second current blocking layer 57, a semiconductor laser device as shown in FIG. 4 is obtained.

However, in order to manufacture such a buried-stripe semiconductor laser device, two crystal growth steps are required, which complicates the manufacturing process and makes it difficult to form the element structure with good reproducibility.

In order to solve such a problem, there has been proposed a method of manufacturing a buried stripe type semiconductor laser device in only one crystal growth step (JP-A-64-25590). This semiconductor laser device has a structure as shown in FIG. 5, and is manufactured as follows.

First, a stripe-shaped mesa portion is formed in the <011> direction on the n-GaAs substrate 61 having the (100) plane by an appropriate etching method. Next, the n-
An n-GaAs thin film 62 'and an n-AlGaAs thin film 6 are formed on a GaAs substrate 61 by an appropriate crystal growth method (for example, metal organic chemical vapor deposition).
3 ', GaAs thin film 64', and p-AlGaAs thin film 65 'are sequentially grown. At this time, nG
It comprises an aAs buffer layer 62, an n-AlGaAs first cladding layer 63, a GaAs active layer 64, and a p-AlGaAs second cladding layer 65.
1) A multilayer thin film surrounded by the B side is formed. Further, an n-AlGaAs current blocking layer 66, a p-AlGaAs cladding layer 67, and a p-GaAs cap layer 68 are successively grown so as to embed the multilayer thin film. Finally, by forming an n-side electrode 69 on the back surface of the n-GaAs substrate 61 and a p-side electrode 70 on the surface of the p-GaAs cap layer 68, a semiconductor laser device as shown in FIG. It is.

As described above, if the structure as shown in FIG. 5 is adopted, a buried stripe type semiconductor laser device can be manufactured with high reproducibility in one crystal growth step.

(Problems to be Solved by the Invention) However, when fabricating the buried stripe type semiconductor laser device shown in FIG. 5, the surface of each epi layer sequentially grown on the semiconductor substrate rises along the side surface of the stripe-shaped mesa portion. , Does not become flat. Such a tendency becomes more prominent when a semiconductor laser device using an InP substrate is manufactured.

In the case of a semiconductor laser device using a GaAs substrate, if the epilayer is grown on the GaAs substrate on which the stripe-shaped mesa portion is formed, the crystal growth rate on the (111) B plane is substantially increased. Since it is zero, (11)
1) If the crystal growth is continued after the multilayer thin film surrounded by the plane B is formed on the mesa portion, the growth of the epi layer proceeds so that the step between the GaAs substrate and the mesa portion is reduced. On the other hand, in the case of a semiconductor laser device using an InP substrate,
Since the crystal growth rate on the (111) B plane is much higher than that when a GaAs substrate is used, the growth of the epi layer is continued while maintaining the step between the InP substrate and the mesa portion.
The structure is as shown in the figure.

However, the buried stripe type semiconductor laser device shown in FIG. 6 cannot be mounted with the epi layer side down since the mesa portion is raised. Therefore, there is a problem in that the thermal resistance is increased to be thermally affected, or the mesa portion is damaged at the time of mounting and strain is applied to the active region, thereby lowering reliability.

The present invention solves the above-mentioned conventional problems,
The purpose is not only to obtain stable single transverse mode oscillation with small oscillation threshold current, but also to mount it with the epi layer side down, so that there is no thermal effect and reliability An object of the present invention is to provide a method for manufacturing a buried stripe type semiconductor laser device having excellent reproducibility with good reproducibility.

(Means for Solving the Problems) A method for manufacturing a semiconductor laser device according to the present invention is a method for manufacturing a buried stripe type semiconductor laser device using an InP semiconductor substrate, wherein a first conductive semiconductor device having a (100) plane is provided. Forming a stripe-shaped mesa portion in the <011> direction on the semiconductor substrate of the mold, and forming a double hetero-structure multilayer film including an active layer for laser oscillation on the substrate having the mesa portion formed thereon. A step of sequentially growing the multilayer film on the mesa portion so that the multilayer film is surrounded by {111} planes; and a step of forming a second conductivity type cap layer and the cap layer on the surface of the multilayer film. A step of sequentially growing different surface semiconductor layers, and a step of selectively removing a raised portion of the surface semiconductor layer located above the mesa portion to expose the cap layer and planarize the same. Because of that The above-mentioned object can be achieved.

In the manufacturing method of the present invention, first, a stripe-shaped mesa portion is formed in a <011> direction on a first conductivity type semiconductor substrate having a (100) plane. Here, the <011> direction is
It represents all directions crystallographically equivalent to the [011] direction, including, for example, the [01] direction. Note that a usual photolithography and etching method are used for forming the mesa portion.

Next, on the substrate on which the mesa portion is formed, a multilayer film having a double hetero structure including an active layer for laser oscillation, a cap layer of the second conductivity type, a surface semiconductor layer, and the like are sequentially formed.
At this time, the multilayer film grows on the mesa portion so as to be surrounded by the {111} plane. Here, the {111} plane represents all crystal planes that are crystallographically equivalent to the (111) plane, and includes, for example, the (111) B plane. If necessary, buffer layers, cladding layers, current blocking layers for current confinement, etc.
It may be formed at each appropriate location. Note that a normal crystal growth method, for example, a metal organic chemical vapor deposition method is used for growing these semiconductor layers.

The surface semiconductor layer is usually grown so that its thickness is equal to or greater than the height of the stripe-shaped mesa portion. Further, the surface semiconductor layer needs to have a different composition of constituent elements from the cap layer in order to give a difference in etching rate between the surface semiconductor layer and the cap layer in a later etching step. Furthermore, the surface semiconductor layer
Preferably, it has the same conductivity type as the semiconductor substrate, that is, the first conductivity type, or is semi-insulating.

Then, the raised portion of the surface semiconductor layer located above the mesa portion is removed, and the surface above the mesa portion is the same height or lower than the surfaces on both sides thereof. In order to remove a part of the surface semiconductor layer, ordinary photolithography and etching are used.

(Function) In the manufacturing method of the present invention, after a multilayer film including an active layer, a cap layer, and the like are sequentially grown on a semiconductor substrate provided with a stripe-shaped mesa portion, a surface semiconductor having a different constituent element from the cap layer is formed. Growing the layer gives a difference in etching rate between the cap layer and the surface semiconductor layer.
For this reason, when removing the raised portion of the surface semiconductor layer above the mesa portion in the next step, the cap layer becomes an etching stopper and the raised portion of the surface semiconductor layer is selectively removed, so that the cap layer is exposed. Flattened. Further, a process margin can be given to the etching removal process for planarization.

In addition, since the obtained semiconductor laser device has no raised portion above the mesa portion, no distortion is applied to the mesa portion even when the semiconductor laser device is mounted with the epi layer down, so that no damage is caused. Further, since mounting can be performed with the epi layer facing down, thermal effects such as temperature rise due to heat generation are suppressed.

(Example) An example of the present invention will be described below.

Embodiment 1 FIG. 1 shows an embodiment of a semiconductor laser device of the present invention. This semiconductor laser device was manufactured as follows.

First, an SiO ₂ film 21 was placed on an n-InP substrate 11 having a (100) plane.
Then, the SiO ₂ film 21 was selectively etched by photolithography and a chemical etching method using HF to form a striped etching mask extending in the [011] direction. Next, by a chemical etching method using a mixed solution (3: 1: 1) of H ₂ SO ₄ , H ₂ O ₂ and H ₂ O,
The n-InP substrate 11 is selectively etched, and FIG.
Inverted mesa-shaped ridge as shown in (1.8 μm high, 3 μm wide)
m) was formed.

After the etching mask is removed, the n-InP thin film 12 '(thickness 0.7 μm) and Ga _0.24 In are deposited on the n-InP substrate 11 on which the mesa portion is formed by metal organic chemical vapor deposition.
_0.76 As _0.55 P _0.45 thin film 13 ′ (0.1 μm thick) was sequentially grown. At this time, on the mesa portion, as shown in FIG. 2 (b), the cross section perpendicular to the resonator direction is trapezoidal, and a multilayer film of a double hetero structure surrounded by the (111) B plane. That is, a multilayer film was formed such that the slope was the (111) B plane grown from both ends of the mesa portion. This multilayer film is composed of an n-InP buffer device 12 and Ga _0.24 In _0.76 As _0.55 P
_0.45 active layer 13.

Subsequently, the p-InP cladding layer 14 (2.0 μm thick), p-Ga
_0.53 In _0.47 As cap layer 15 (0.5 μm thickness) and nI
An nP surface semiconductor layer 16 (1.8 μm in thickness) was sequentially grown.
As crystal growth proceeds on both sides of the mesa, (111) B
Crystal growth occurred at a uniform rate on all surfaces including the surface, and a buried stripe structure as shown in FIG. 2 (b) was obtained.

Next, as shown in FIG. 2 (c), the raised portion of the n-InP surface semiconductor layer 16 located above the mesa portion is selectively etched and removed by photolithography and chemical etching. And height are aligned. By using a mixed solution of HCl and H ₂ O (4: 1) as an etchant, p-Ga _0.53 In _0.47 As cap layer 1
It was possible to etch only the n-InP surface semiconductor layer 16 without etching 5.

Finally, an SiO ₂ insulating film 17 is deposited on the entire surface, and a stripe portion of the SiO ₂ insulating film 17 serving as a current injection region is removed by etching. Then, an n-side electrode 18 is formed on the back surface of the n-InP substrate 11. SiO ₂
The surface of the insulating film 17 and the p-Ga
By forming a p-side electrode 19 on the surface of the _0.53 In _0.47 As cap layer 15, a buried stripe type semiconductor laser device as shown in FIG. 1 was obtained.

A buried-stripe semiconductor laser device was fabricated in the same manner as described above except that the inverted mesa-shaped ridge had a small width of about 1.5 μm. However, the device structure could be formed with good reproducibility. Was.

The semiconductor laser device of the present embodiment thus obtained can be mounted with the surface above the mesa portion being the same height or lower than the surfaces on both sides thereof and the epi layer side down. Therefore, thermal effects such as temperature rise due to heat generation were suppressed, and good device characteristics were exhibited.

Embodiment 2 FIG. 3 shows another semiconductor laser device of the present invention. This semiconductor laser device was manufactured as follows.

First, in the same manner as in the first embodiment, nI having a (100) plane
An inverted mesa-shaped ridge (1.8 μm high and 3 μm wide) is placed on the nP substrate 31.
m) was formed. Next, the n-InP with the mesa formed
An n-InP thin film 32 ′ (thickness 0.7 μm) and a Ga _0.24 In _0.76 As _0.55 P _0.45 thin film 33 ′ (thickness 0.1) were formed on the substrate 31 by metal organic chemical vapor deposition in the same manner as in Example 1. μm) were grown sequentially. At this time, on the mesa portion, as shown in FIG. 3, the cross-sectional shape perpendicular to the resonator direction is trapezoidal, and the multilayer film of the double hetero structure surrounded by the (111) B plane, that is, its slope Was formed as a (111) B plane grown from both ends of the mesa portion. This multilayer film is composed of an n-InP buffer layer 32, Ga _0.24 In _0.76 As _0.55 P
_0.45 active layer 33.

Subsequently, the p-InP cladding layer 34 (thickness 1.0 μm), n-InP
P current blocking layer 35 (thickness 0.5 μm), p-InP cladding layer 36 (thickness 1.0 μm), p-Ga _0.53 In _0.47 As cap layer 35 (thickness 0.5
μm) and an n-InP surface semiconductor layer 38 (1.8 μm in thickness) were sequentially grown.

Next, the protruding portion of the n-InP surface semiconductor layer 38 located above the mesa portion was selectively etched and removed by photolithography and chemical etching, and the height was made equal to both sides. Note that a mixed solution of HCl and H ₂ O (4: 1) was used as an etchant.

Finally, an SiO ₂ insulating film 39 is deposited on the entire surface, and a stripe portion serving as a current injection region is removed by etching. Then, Zn is diffused into the stripe portion to form a Zn diffusion region 40, and a position above the mesa portion is formed. The conductivity type of the portion of the n-InP current blocking layer 35 to be formed is inverted to p-type, and the n-side electrode 41 is exposed on the back surface of the n-InP substrate 31, and is exposed on the surface of the SiO ₂ insulating film 39 and its stripe portion. By forming a p-side electrode 42 on the surface of the Zn diffusion region 40, a buried stripe type semiconductor laser device as shown in FIG. 3 was obtained.

In the semiconductor laser device of this embodiment, an n-InP current blocking layer 35 is provided, and the conductivity type of the portion above the mesa portion is inverted to p-type by Zn diffusion. Therefore, this pn
The injection current is more reliably constricted by the inversion portion,
The oscillation threshold current is further reduced.

In the above embodiment, the conductivity type of the semiconductor substrate (that is, the first conductivity type) is n-type, and the conductivity type of the cap layer (that is, the second conductivity type) is p-type. The conductivity type may be p-type and the second conductivity type may be n-type. Furthermore, although the [011] direction is selected as the direction for forming the stripe-shaped mesa portion on the semiconductor substrate, the same effect can be expected even in the [01] direction that is crystallographically equivalent.

In the above embodiment, an InP-GaInAsP-based buried stripe semiconductor laser device has been described.
AlGaAs-based buried stripe semiconductor laser devices,
The manufacturing method of the present invention can be similarly applied to a buried-stripe semiconductor laser device using another compound semiconductor including a multi-element mixed crystal system.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, even when an InP semiconductor substrate is used, the rise of the surface semiconductor layer above the mesa portion can be achieved by using the cap layer as an etching stopper. The portion can be selectively removed and flattened. Further, a process margin can be given to the etching removal process for planarization.
As a result, a buried-stripe semiconductor laser device having a small oscillation threshold current and capable of stable single transverse mode oscillation can be obtained with good reproducibility. In this semiconductor laser device, since there is no raised portion above the mesa portion, the semiconductor laser device can be mounted with the epi layer side down without applying distortion or damage to the mesa portion. Therefore, thermal effects such as temperature rise due to heat generation are suppressed, and reliability is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the semiconductor laser device of the present invention, FIGS. 2 (a) to 2 (c) are sectional views showing a manufacturing process of the semiconductor laser device of FIG. 1, and FIG. FIG. 4, FIG. 5, FIG. 6, and FIG. 6 are cross-sectional views showing a conventional buried stripe type semiconductor laser device, respectively, showing another embodiment of the semiconductor laser device of the present invention. 11,31 …… n-InP substrate, 12,32 …… n-InP buffer layer, 13,33
…… Ga _0.24 In _0.76 As _0.55 P _0.45 active layer, 14,34,36 …… p-In
P cladding layer, 15,37 …… p-Ga _0.53 In _0.47 As cap layer, 1
6,38 …… n-InP surface semiconductor layer, 17,39 …… SiO ₂ insulating film, 18,4
1 ... n-side electrode, 19, 42 ... p-side electrode, 35 ... n-InP current blocking layer, 40 ... Zn diffusion region.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Haruhisa Takiguchi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-2-268482 (JP, A)

Claims (1)

(57) [Claims] 1. A method of manufacturing a buried stripe type semiconductor laser device using an InP semiconductor substrate, comprising the steps of: forming (0) on a semiconductor substrate of a first conductivity type having a (100) plane;
Forming a stripe-shaped mesa portion in the <11>direction; and forming a double hetero-structure multilayer film including an active layer for laser oscillation on the substrate on which the mesa portion is formed, and forming the multilayer film on the mesa portion. Successively growing such that is surrounded by {111} planes; and sequentially growing a cap layer of the second conductivity type and a surface semiconductor layer having a different constituent element from the cap layer on the surface of the multilayer film. A method of manufacturing a semiconductor laser device, comprising the steps of: selectively removing a raised portion of the surface semiconductor layer located above the mesa portion, exposing the cap layer, and flattening the cap layer.