JPH0645704A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for a highly reliable low-threshold semiconductor laser device, with which stabilized single mode oscillation can be obtained. CONSTITUTION:This semiconductor laser device manufacturing method is composed of the steps of growing a current block layer 2 and growing a semiconductor layer having a double heterostructure containing an active layer 5. By growing the current block layer 2 and a regrowth interface control layer 3 by the first growth process, the reverse-biased interface can be prevented from becoming a regrown interface. Accordingly, as a current constricting structure can be formed stably, a reactive current can be reduced. Also, as the angle between the side face and the bottom face of the double heterostructure including the active layer becomes about 54.7 deg. which is the angle formed by the (111) B surface and (100) surface, the semiconductor layer of about 1.5 to 2mum can be formed in an excellent reproducible manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a buried stripe type semiconductor laser device having a current constriction structure.

[0002]

2. Description of the Related Art In recent years, a semiconductor laser device capable of coherent optical oscillation by stimulated emission has attracted attention as a light source in the fields of optical information processing, optical measurement and optical communication.
In this field, high reliability, low drive current are required for characteristics such as high output, high efficiency, and high speed modulation. For such a semiconductor laser device, it is an important condition that the oscillation threshold current is low and a stable oscillation transverse mode can be obtained.

Many reports have hitherto been made on the structure for controlling the oscillation transverse mode. Generally, a semiconductor laser device with a Fabry-Perot resonator structure is a gain waveguide type with a current confinement path, a built-in refractive index waveguide type with a refractive index distribution perpendicular to the cavity direction, and a waveguide side surface. It is roughly classified into a refractive index waveguide type in which is embedded. To achieve stabilization of oscillation transverse mode and reduction of oscillation threshold current,
There is a need for a structure that suppresses the spread of the injection current so that the injection current concentrates in a narrow region near the active layer that generates laser light and that efficiently confine the laser light in the narrow region. As a semiconductor laser device having such a structure, there is a buried stripe type semiconductor laser device.

FIG. 2 shows a conventional buried stripe type semiconductor laser device. This semiconductor laser device includes a substrate 21, an n-type InP first cladding layer 22, and a non-doped GaIn layer.
A stripe 20 composed of an AsP active layer 23 and a p-type InP second cladding layer 24 is laminated. A p-type InP current blocking layer is formed on the substrate 21 so as to fill the stripe 20.
25, n-type InP current blocking layer 26 is laminated, and p
The junction surface between the type current block layer 25 and the n-type current block layer 26 is almost at the same height as the active layer 23. Stripe 20
And p-type In on the n-type InP current blocking layer 25.
A P layer 27 and a p-type GaInAsP contact layer 28 are laminated. An n-side AuGe electrode 30 is provided on the back surface of the substrate 21, and a p-side AuZn electrode is provided on the front surface of the p-type contact layer 28.
An electrode 29 is provided.

Cladding layers 22 and 24 forming the stripe 20
Are in contact with current blocking layers 25, 26 of opposite conductivity type. Therefore, when a voltage is applied, a bias voltage is applied to the current blocking layers 25 and 26 in the direction opposite to that of the stripe 20, and a reactive current that does not contribute to laser oscillation flows through the current blocking layers 25 and 26. Is suppressed, and the current efficiency of the semiconductor laser device is improved. As a result, the oscillation threshold current can be lowered. Further, since the current blocking layers 25 and 26 are made of a semiconductor material having a band gap smaller than that of the active layer 23, in the active layer 23, an equivalent refractive index difference occurs in a direction parallel to the bonding surface, and stripes are formed.
Below 20, the equivalent refractive index increases and the light emitting region is confined. Therefore, single transverse mode oscillation is obtained.

However, in order to cause this semiconductor laser device to oscillate in a single transverse mode, the width of the active layer 23 should be about 1.5-2.
It is necessary to form it to a μm. Stripe containing active layer 23
Since 20 is usually formed by removing the peripheral portion by wet etching, it was difficult to form a uniform width even within the wafer with high precision. Further, when manufacturing the semiconductor laser device described above, there are three steps of a step of forming the stripe 20, a step of embedding the stripe 20 between the current block layers 25 and 26, and a step of forming a contact layer.
Since the crystal growth process was required twice, the manufacturing process was complicated. Furthermore, when stacking the current block layers 25 and 26, it was difficult to align the junction surfaces of the current block layers 25 and 26 with the same height as the active layer 23.

In order to solve the above problems, a semiconductor laser device as shown in FIG. 3 has been proposed. This semiconductor laser device is manufactured as follows.

First, <011> is formed on the n-type InP substrate 31.
A stripe mask made of Al ₂ O ₃ and having a width of about 3 to 5 μm is formed along the direction, and a stripe-shaped convex portion 37 having a width of about 3 to 5 μm is formed by a chemical etching method using H ₂ SO ₄ . At this time, the side surface of the stripe-shaped convex portion 37 is (22
It is composed of 1) plane and (111) plane.

Next, with the above mask left, metal oxide vapor phase epitaxy (MOCVD) is performed so that the thickness of the flat portions on both sides of the stripe-shaped convex portion becomes 0.5 to 1.0 μm.
The type InP current blocking layer 32 is laminated. At this time, the substrate 31
All parts except the above mask above the current block layer 32
Is covered with.

After removing the mask using an HF solution, the n-type InP first cladding layers 33a and 33b and the non-doped GaInAsP active layers 34a and 33 are formed by a low pressure MOCVD method.
b, p-type InP second cladding layer 35 and p-type GaInA
The sP contact layer 36 is sequentially laminated.

Then, on the back surface of the n-type substrate 31, the n-side AuG is formed.
The e-electrode 39 is formed on the surface of the p-type contact layer 36 by the p-side AuZ.
A semiconductor laser device is obtained by forming the n-electrode 38.

In this semiconductor laser device, on the stripe-shaped convex portion 37, the cross section in the direction perpendicular to the resonator from which light is emitted is trapezoidal and the side surface is the (111) B plane.
The mold first clad layer 33a and the active layer 34a are formed. Further, as the n-type first clad layer 33b, the active layer 34b, the p-type second clad layer 35 and the p-type GaInAsP contact layer 36 are laminated, the n-type first clad layer formed on the stripe-shaped convex portion 37 is formed. The clad layer 33a and the active layer 34a are embedded in the p-type second clad layer 35. n-type first cladding layer 33
The angle formed by the side surface of a and the active layer 34a with the bottom surface is (1
11) The angle between the B surface and the (100) surface is about 54.7 °,
Since the crystal structure is determined, the layers can be laminated with high accuracy. Therefore, the width of the stripe-shaped convex portion 37 is 3 to 5 μm.
The width of the active layer 34 can be reproducibly set to 1.5 to 2 μm and single transverse mode oscillation can be obtained.

In this semiconductor laser device, the reduced pressure M
Since the semiconductor layer having the double hetero structure including the active layer 34 is formed by using the OCVD method, the width of the active layer 34 can be accurately reproduced. Further, since the p-type current blocking layer 32 is previously laminated on the n-type substrate 31, after that, the n-type first cladding layers 33a and 33b, the active layers 34a and 33b, the p-type second cladding layer 35 and the p-type second cladding layer 35 and A buried stripe type semiconductor laser device can be easily obtained only by sequentially stacking the contact layers 36.

[0014]

In the above semiconductor laser device, since the p-type semiconductor layer is used as the current block layer 32, the p-type current block layer 32, which is the regrowth interface, and the n-type InP first cladding. The interface with the layer 33b is a reverse bias interface. On the other hand, at the regrowth interface, oxidation and adhesion of impurities easily occur, and it is difficult to obtain a good interface. Therefore, the leak current increases and, as a result, the threshold current increases, leading to an increase in drive current and unstable oscillation.

The present invention is intended to solve the above problems, and an object thereof is a method of manufacturing a semiconductor laser device having a low threshold current and stable single transverse mode oscillation, which is excellent in reliability. To provide.

[0016]

A method of manufacturing a semiconductor laser device according to the present invention is a method of manufacturing a buried stripe type semiconductor laser device having a current confinement structure, comprising:
A step of forming a stripe-shaped convex portion on a substrate having a (0) plane so that the longitudinal direction of the stripe coincides with the <011>direction; and on the substrate other than the upper surface of the convex portion,
A first growth step of growing a current blocking layer for current confinement and a re-growth interface control layer in this order, and an activity in which trapezoidal stripes are formed on the upper surfaces of the convex portions and side surfaces are {111} B surfaces. A second growth step of growing a light emitting portion including a layer so that the light generating portion is in a buried state, whereby the above object is achieved.

[0017]

A buried stripe type semiconductor laser device having a current confinement structure has a step of forming a stripe-shaped convex portion and then growing a current block layer, and a semiconductor of a double hetero structure including an active layer on the convex portion. The device structure is completed by two growth steps including the step of growing the layer.
Therefore, a regrowth interface is formed between the first growth step and the second growth step. In the method for manufacturing a semiconductor laser device of the present invention, the reverse bias interface can be formed in the first growth step by stacking the current block layer and the regrowth interface control layer in the first growth step. Therefore, this reverse bias interface can be prevented from becoming a regrowth interface. Therefore, since the current confinement structure can be firmly formed, the reactive current that does not contribute to laser oscillation can be reduced and the threshold current can be lowered.

In the second growth step, the angle between the side surface and the bottom surface of the laminated structure including the active layer formed on the convex portion is formed by the (111) B plane and the (100) plane. The angle is about 54.7 °, which allows for accurate stacking. Therefore, the active layer width can be formed with a reproducibility of 1.5 to 2 μm, and stable single transverse mode oscillation can be obtained.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

1A to 1C are views showing a method of manufacturing a semiconductor laser device according to a first embodiment of the present invention.

A method of manufacturing this semiconductor laser device will be described below. First, as shown in FIG. 1A, an amorphous dielectric film made of Si ₃ N ₄ having a thickness of 0.1 to 0.3 μm is formed on a (100) plane of a Sn-doped n-type InP substrate 1 by using a plasma CVD method. Form the body film 12, by a normal photo-etching process,
On the dielectric film 12, a groove having a width of 5 μm reaching the substrate 1 was formed along the <011> direction. Next, H ₂
Stripe-shaped projections 11 having a width of about 3 to 5 μm were formed by a chemical etching method using a SO ₄ + H ₂ O ₂ based solution. At this time, the side surface of the stripe-shaped convex portion 11 is composed of the (221) plane and the (111) plane.

Next, as shown in FIG. 1B, the thickness of the flat portions on both sides of the stripe-shaped convex portion 11 is 0.5 by MOCVD while the mask made of the dielectric film 12 is left.
The Zn-doped p-type InP current blocking layer 2 is laminated to have a thickness of 0.1 μm to 1.0 μm, and then Si is made to have a thickness of 0.1 to 0.3 μm at the flat portions on both sides of the stripe-shaped convex portion 11.
A doped n-type InP regrowth interface control layer 3 was laminated. At this time, the current blocking layer 2 and the regrown interface control layer 3 are all covered on the substrate 31 except the above-mentioned mask. The above is the first growth step.

After that, an HF solution was used to produce the above dielectric film.
The mask made of 12 is removed, and by the low pressure MOCVD method,
Si-doped n-type InP first cladding layers 4a, 4b, non-doped GaInAsP active layers 5a, 5b, Zn-doped p-type InP
The second cladding layer 6, the Zn-doped p-type GaInAsP contact layer 7 and the Si-doped InP flattening layer 8 were sequentially stacked. The above is the second growth step. Next, using the resist or the dielectric film as a mask, the planarization layer 8 is removed by etching to planarize the upper surface. As an etching solution, HCl having a high selectivity between InP and GaInAsP:
The contact layer 7 was made to stop etching by using a H ₂ O = 4: 1 solution.

Finally, as shown in FIG. 1C, an n-side AuGe / Ni electrode 10 is provided on the back surface of the n-type substrate 1, and a p-side AuZn / Au electrode 9 is provided on the surface of the p-type contact layer 7. A semiconductor laser device was obtained by forming.

In this semiconductor laser device, an n-type first portion having a trapezoidal cross section in a direction perpendicular to a resonator for emitting light and a side surface of (111) B plane is formed on the stripe-shaped convex portion 11. A clad layer 4a and an active layer 5a are formed. The angle formed by the side surfaces of the n-type first cladding layer 4a and the active layer 5a with the bottom surface thereof is about 54.7 ° which is the angle formed by the (111) B plane and the (100) plane, and is determined by the crystal structure.
It can be laminated with high precision. Therefore, by forming the stripe-shaped convex portions 11 to have a width of 3 to 5 μm, the width of the active layer 34 can be reproducibly set to 1.5 to 2 μm, and a single transverse mode oscillation with an emission wavelength of 1.3 μm can be achieved. I was able to get

Further, in this method for manufacturing a semiconductor laser device, the reverse bias interface is formed in the first growth step, so the reverse bias interface does not become a re-growth interface. Therefore, the reactive current that does not contribute to the laser oscillation can be reduced, and the threshold current can be lowered to 10 mA or less.

Although the n-type InP substrate is used as the semiconductor substrate in this embodiment, a p-type substrate can be used. As the semiconductor layer, in addition to the InP-GaInAsP system, AlGaAs system or the like can be used. Also,
As a method for growing the semiconductor layer, the MBE method or the ALE method can be used.

DH in which an active layer is sandwiched by a pair of clad layers
Not only (double heterostructure) structure, but for example,
SC with an optical guide layer inserted between the active layer and the cladding layer
GRIN- with H (separated confiment heterostructure) structure and further GRIN (graded index) layer inserted
An SCH structure or the like can also be adopted. Further, the active layer may have a multiple quantum well structure.

[0029]

According to the present invention, the reverse bias interface can be prevented from becoming a re-growth interface, so that the current confinement structure can be firmly formed and the reactive current that does not contribute to laser oscillation can be reduced. Therefore, the threshold current can be lowered. Moreover, since a narrow active layer can be formed with high accuracy and reproducibility, stable single transverse mode oscillation can be obtained. Therefore, a semiconductor laser device having excellent oscillation characteristics can be manufactured with high yield.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing method of an embodiment of a semiconductor laser device of the present invention.

FIG. 2 is a vertical cross-sectional view showing a conventional semiconductor laser device.

FIG. 3 is a vertical sectional view showing a conventional semiconductor laser device.

[Explanation of symbols]

 1 Sn-doped n-type InP substrate 2 Zn-doped p-type InP current blocking layer 3 Si-doped n-type InP regrowth interface control layer 4a, 4b Si-doped n-type InP first cladding layer 5a, 5b Non-doped GaInAsP active layer 6 Zn-doped p Type InP second clad layer 7 Zn-doped p-type GaInAsP contact layer 8 Si-doped InP flattening layer 9 p-side AuZnAu electrode 10 n-side AuGe / Ni electrode 11 stripe-shaped convex portion 12 dielectric film

Claims (2)

[Claims] 1. A method of manufacturing a buried stripe type semiconductor laser device having a current confinement structure, wherein a stripe-shaped convex portion is formed on a substrate having a (100) plane, and the longitudinal direction of the stripe is the <011> direction. And a first growth step of growing a current blocking layer for current confinement and a regrowth interface control layer in this order on the substrate other than the upper surface of the convex portion, The upper surface of the convex portion has a trapezoidal stripe shape, and the side surface is {1.
11} A method of manufacturing a semiconductor laser device, comprising: a second growth step of growing a light emitting portion including an active layer having a B-plane so that the light generating portion is in a buried state. 2. The manufacturing method according to claim 1, wherein the substrate has a first conductivity type, the current blocking layer has a conductivity type opposite to the first conductivity type, and the regrowth interface control layer has a first conductivity type.