JPH06350188A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To increase accuracy of the width of a third clad layer and stabilize threshold current at oscillation start. CONSTITUTION:A semiconductor laser element has a structure formed by laminating a substrate 1, a first clad layer 2, an activating layer 3 and a second clad layer 4, a third clad layer 5, a fourth clad layer 9 and contact layer 6 in such order and by burying current bottlenecking layers 8 on 1 both side planes of the third clad layer 5 which is a stripe-shaped mesa part. Especially the thickness of the third clad layer 5 is permitted to be small within a range of 0.2-0.5mum, and an etching depth, which has been conventionally approximately 1.5mum including a contact layer, is reduced. Therefore, the width of the third clad layer 5 is accurately reduced to a desired size, and laser beam oscillation is stabilized by forming the fourth clad layer 9 and the contact layer 6 at the third deposition process to deal with the thinned third clad layer 5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a Al _X Ga _1-x As based semiconductor laser device.

[0002]

2. Description of the Related Art Al _X Ga _1-x that oscillates in a single transverse mode
An As-based (0 ≦ X ≦ 1) semiconductor laser device having a structure shown in FIG. 3 is known. FIG. 3 is a schematic sectional view of this semiconductor laser device as seen from the front. As shown in FIG. 3, this device includes a first clad layer 2, an active layer 3, a second clad layer 4, and a third clad layer 5 on a GaAs substrate 1.
And the contact layer 6 are laminated in this order.
Both sides of the stripe-shaped mesa portion formed in the clad layer 5 and the contact layer 6 parallel to the laser light emission direction are filled with the current confinement layer 8. The current confinement layer 8 has a role of absorbing laser light, and by appropriately setting the width of the third cladding layer 5, stable transverse mode oscillation of the device is possible, and the current confinement layer 8 is activated. Since it is close to the light emitting region of the layer 3, the current concentrates in a part of the active layer 3 and the oscillation threshold current can be lowered.

Such a semiconductor laser device usually has the following structure.
Manufactured in this way. 4 (a) to 4 (d) show the main
FIG. 4 is a manufacturing process chart showing the same process sequence as that of FIG.
It is represented by a single code. First, the n-type GaAs substrate 1 (S
i-doped, carrier concentration 2 × 10¹⁸/ Cm³, Thickness 30
MOCVD (Metal Organic Chemical Vapor Deposition) method
The first cladding layer 2 (n-type Al_0.5Ga_0.5As,
Carrier concentration 5 × 10¹⁷/ Cm³, Thickness 1 μm), active
Layer 3 (undoped, Al_0.1Ga_0.9As, thickness 0.1
μm), second cladding layer 4 (p-type Al_0.5Ga_0.5A
s, carrier concentration 5 × 10¹⁷/ Cm ³, Thickness 0.3μ
m), the third cladding layer 5 (p-type Al_0.5Ga_0.5As,
Carrier concentration 5 × 10¹⁷/ Cm³, Thickness 1.0 μm),
Contact layer 6 (p-type GaAs, carrier concentration 1 × 10
¹⁹cm³, 0.5 μm thick) [Fig. 4
(A)].

Next, S is sputtered on this wafer.
An iO ₂ film 7 is attached, a photoresist is applied and patterning is performed to form a stripe having a width of 5 μm on the contact layer 6. Then, the contact layer 6 is formed by using a phosphoric acid-based etching solution with the photoresist as a mask.
Then, a part of the third cladding layer 5 is etched. [FIG.4 (b)].

Next, after removing the photoresist, the current confinement layer 8 (n-type GaAs, carrier concentration 1 × 10 ¹⁹ / cm ³ , thickness 1.0 μm) is grown again by MOCVD method [FIG. )]. Subsequently, this is taken out of the apparatus, the SiO ₂ film 7 is removed, and then the contact layer is regrown by 5 μm by the MOCVD method to form the contact layer 6 so as to be integrated with the initial contact layer [FIG.
(D)].

After that, upper and lower p and n electrodes (not shown) are formed, and the wafer is cleaved into chips to obtain a semiconductor laser device having the structure shown in FIG.

[0007]

However, the semiconductor laser device manufactured as described above has the following problems. It is the MOCV again in the process of FIG. 4 (c).
It is difficult to control the width of the third clad layer 5 when the current confinement layer 8 is grown by the D method because the etching depth is as deep as 1.5 μm. By this,
The variation in the oscillation start threshold current greatly depends on the width dimension of the third cladding layer 5, which is a problem when mass-producing semiconductor laser devices. In order to control the width dimension of the third cladding layer 5 with high accuracy, the thickness of the third cladding layer 5 may be reduced. However, in this case, the confinement of the light oscillated in the active layer 3 is weakened and the oscillation starts. This causes a problem that the threshold current increases. Thus, conventionally, it was very difficult to control the width dimension of the third cladding layer 5 and manufacture a semiconductor laser device that oscillates at a low threshold current.

The present invention has been made in view of the above points, and an object thereof is to provide a semiconductor laser device in which the variation in the width dimension of the third cladding layer is reduced and a stable oscillation threshold current can be obtained. To do.

[0009]

In order to solve the above-mentioned problems, a semiconductor laser device of the present invention comprises a first clad layer (2) and an active layer which are sequentially laminated on one main surface of a GaAs substrate (1). (3), the second cladding layer (4), and the third cladding layer (5), G on the second cladding layer (4)
A mesa portion in which the aAs layer (10) is laminated in this order and formed in a stripe shape, and a current confinement layer (8) having a conductivity type opposite to that of the third clad layer (5) embedded on both sides of the mesa portion.
A fourth cladding layer (9) formed on the same plane formed by the upper surface of the mesa portion and the upper surface of the current confinement layer (8), and the fourth cladding layer (9).
The structure has a contact layer (6) laminated on the clad layer (9).

[0010]

The semiconductor laser device of the present invention is constructed as described above, and the third clad layer has a thickness of 0.2 to
The etching depth when etching the region where the current constriction layer is grown without forming a contact layer in the initial growth process is also 0.2 to 0.5 μm.
Since the depth is made as shallow as about 0.5 μm, the variation in the width dimension of the third cladding layer due to this etching can be reduced, and therefore the variation in the oscillation threshold current of the obtained device is also reduced. . Moreover, in contrast to the thin third cladding layer, the fourth cladding layer and the contact layer are laminated in the third growth process to stabilize the oscillation of the laser light.

[0011]

EXAMPLES The present invention will be described below based on examples. The structure of the semiconductor laser device of the present invention is shown in the schematic sectional view of FIG. 1, and the portions common to FIG. The semiconductor laser device of the present invention is different from the conventional one in that, as shown in FIG. 1, the thickness of the third cladding layer 5 is smaller than that of the conventional device.
The fourth clad layer 9 is newly added.

The semiconductor laser device of the present invention can be manufactured as follows. The main process steps are shown in the manufacturing process diagrams of FIGS. 2 (a) to 2 (c). The same symbols are used. First, as in FIG. 4A, n-type G
On the aAs substrate 1, the first clad layer 2, the active layer 3, the second clad layer 4, the third clad layer 5 (p-type Al _0.5 Ga _0.5 As, carrier concentration 5 × 10) are formed by MOCVD.
¹⁷ / cm ³ , thickness 0.3 μm, GaAs layer 10 (p-type GaAs, carrier concentration 1 × 10 ¹⁸ cm ³ , thickness 0.0
3 μm). In this process, the thickness of the third cladding layer 5 is set to 0.3 μm, and the contact layer 6 is not formed, which is different from the conventional case. [FIG. 2 (a)].

Next, by a method similar to that shown in FIGS. 4A and 4B, the region where the current confinement layer 8 is grown is etched to form a stripe shape composed of the third cladding layer 5 and the GaAs layer 10. The mesa portion is formed, and the current confinement layer 8 is buried on both side surfaces thereof. At this time, the GaAs layer 10 is used to prevent the surface of the third cladding layer 5 from being oxidized. Therefore, the thickness of the current confinement layer 8 is the third
The clad layer 5 (0.3 μm) and the GaAs layer 10 (0.0
3 μm), which is a total thickness of 0.33 μm, and the etching depth for forming the stripe-shaped mesa portion can be made shallow, which is also a point different from the conventional one [FIG.
(B)].

Subsequently, SiO not shown here is used.₂film
After removing the ash, the fourth crack was formed by the third MOCVD method.
Layer 9 (p-type Al_0.5Ga_0.5As, carrier concentration 5 ×
10 ¹⁷/ Cm³, Thickness 0.7 μm). Fourth
The clad layer 9 can be formed by keeping the third clad layer 5 thin.
This is because light is absorbed and laser oscillation does not occur.
Must be formed in order to compensate for
is there. Then, the contact layer 6 is grown to 5 μm [FIG.
(C)].

After that, the upper and lower p and n electrodes are formed in the same manner as in the conventional case, and the wafer is cleaved into chips to obtain the semiconductor laser device shown in FIG. 1 (the upper and lower electrodes are not shown). Obtainable. The oscillation start threshold currents of 100 semiconductor laser devices of the present invention obtained as described above and 100 conventional semiconductor laser devices were measured and compared. As a result, the oscillation start threshold current of the semiconductor laser device of the present invention was 36 mA ± 2 mA, whereas the oscillation start threshold current of the conventional semiconductor laser device was 37.5 mA ± 8 mA. . Furthermore, the third
The width of the clad layer 5 was measured and found to be 3.9 μm ± 0.02 μm for the device of the present invention and 3.9 for the conventional device.
It was 5 μm ± 0.43 μm. Thus, it is understood that the semiconductor laser device of the present invention has improved controllability of the width dimension of the third cladding layer 5.

In this embodiment, the case where the thickness of the third cladding layer 5 is set to 0.3 μm has been described, but the same effect can be obtained up to a thickness of 0.5 μm. it can. The lower limit of the thickness of the third cladding layer 5 can be determined in relation to the current confinement layer 8. If the thickness is less than 0.2 μm, the current confinement layer 8 cannot play the role of narrowing the current. Therefore, the third cladding layer 5 of the device of the present invention
An appropriate thickness range for the can be determined from 0.2 μm to 0.5 μm.

Regarding other characteristics, it was found that the device of the present invention exhibits good characteristics equivalent to or better than those of the prior art.

[0018]

In the current confinement type semiconductor laser device, the etching depth is large when the region where the current confinement layer is formed is etched, so that the width of the third clad layer varies and the oscillation start threshold is generated. Although the variation of the value current was large, in the present invention, as described in the embodiment, the thickness of the third cladding layer is reduced to the range of 0.2 to 0.5 μm, and the conventional contact layer including 1. Since the etching depth was reduced to about 5 μm, the third clad layer can be accurately made to have a desired width dimension, and the third clad layer is thin. By providing the fourth clad layer in the MOCVD growth process and forming the clad layer on the fourth clad layer, the variation of the oscillation start threshold current depending on the width of the third clad layer is reduced. As a result, the semiconductor laser device of the present invention can oscillate laser light in a stable transverse mode.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a structure of a semiconductor laser device of the present invention.

FIG. 2 shows a main manufacturing process sequence of the semiconductor laser device of the present invention, in which (a) is the initial stacking process, (b) is the process of filling the current constriction layer after etching, and (c) is the fourth cladding. Cross-sectional view showing the process of forming the contact layer and contact layer

FIG. 3 is a schematic sectional view showing the structure of a conventional semiconductor laser device.

FIG. 4 shows a main manufacturing process sequence of a conventional semiconductor laser device, in which (a) is an initial stacking process, (b) is an etching process, and (c) is a process of embedding a current constriction layer.
(D) A schematic cross-sectional view showing a process of forming a contact layer

[Explanation of symbols]

1 Substrate 2 First Cladding Layer 3 Active Layer 4 Second Cladding Layer 5 Third Cladding Layer 6 Contact Layer 7 SiO ₂ Film 8 Current Constriction Layer 9 Fourth Cladding Layer 10 GaAs Layer

Claims (2)

[Claims] 1. A sequentially stacked A on a main surface of a GaAs substrate
l _X Ga _1-X As first cladding layer, Al _Y Ga _1-Y As
Active layer [0 ≦ Y ≦ X ≦ 1 (the same applies below)], Al _X Ga
_1-X As 2nd clad layer and A on this 2nd clad layer
l _X Ga _1-X As third clad layer and GaAs layer are laminated in this order to form a stripe-shaped mesa portion, and the Al _X Ga _1-X As third portion embedded on both sides of the mesa portion.
A current confinement layer having a conductivity type opposite to that of the clad layer, an Al _X Ga _{1 -X} As fourth clad layer laminated on the same plane formed by the upper surface of the mesa portion and the upper surface of the current confinement layer, and the fourth clad. And a GaAs contact layer laminated on the layer. 2. The semiconductor laser device according to claim 1, wherein the Al _x Ga ₁ -x As third cladding layer has a thickness of 0.2.
A semiconductor laser device having a thickness of 0.5 μm.