JPH0669591A - Manufacture of semiconductor laser element - Google Patents

Abstract

PURPOSE:To grow a third clad layer without oxidizing the surface of a second clad layer, and improve crystallinity, by a method wherein a thinnly left layer of a current constriction layer is vaporized until it reaches the second clad layer, by performing heat treatment in an AsH atmosphere before the third clad layer is formed. CONSTITUTION:A current constriction layer 7 above an active layer 3 which corresponds to a light emitting region is so etched that a thin layer 7a is formed while the layer 7 of about 0.057mu in thickness is left. After photoresist 10 which has been used for patterning is eliminated, the element is put in an MOCVD equipment while the thin layer 7a is left as it is, and heat treatment at 900-1050 deg.C is performed for 60 minutes in an arsine atmosphere wherein the partial pressure of AsH4 is 3X10<-4>. Thereby the thin layer 7a left in the current constriction layer 7 is vaporized, and a clean surface of the second clad layer 4 is exposed, so that troubles due to an surface oxide film on the second clad layer are not generated.

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 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. 1 is known. FIG. 4 is a schematic sectional view of this semiconductor laser device as seen from the front. As shown in FIG. 4, this device comprises 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 side surfaces of the clad layer 5 formed in a stripe shape parallel to the laser light emission direction are filled with the current confinement layer 7. The current confinement layer 7 has a role of absorbing laser light, and by appropriately determining the width of the third cladding layer 5, stable transverse mode oscillation of the device is possible, and the current confinement layer 7 is activated. Since the current is concentrated in a part of the active layer 3 because it is close to the light emitting region of the layer 3, the oscillation threshold current can be lowered. 8 is the upper electrode, 9
Is the lower electrode.

Such a semiconductor laser device usually has the following structure.
Manufactured in this way. 5 (a)-(d) are the main
4 is a process chart in which parts common to FIG. 4 are indicated by the same reference numerals.
It First, the n-type GaAs substrate 1 (Si-doped, carrier
Concentration 2 × 10¹⁸/ Cm³, Thickness of 300 μm), MO
First cladding using CVD (metal organic chemical vapor deposition) method
Layer 2 (n-type Al_0.5Ga_0.5As, carrier concentration 5 × 1
0¹⁷/ Cm³, Thickness 1 μm, active layer 3 (non-doped,
Al_0.1Ga_0.9As, thickness 0.1 μm), second crack
Layer 4 (p-type Al_0.5Ga_0.5As, carrier concentration 5 ×
10¹⁷/ Cm ³, Thickness 0.3 μm, current confinement layer 7 (n
Type GaAs, carrier concentration 1 × 10¹⁹/ Cm³,thickness
0.5 μm) are sequentially grown [FIG. 5 (a)].

Next, a photoresist 10 is formed on the wafer.
Is applied and patterned to form a stripe having a width of 5 μm on the current confinement layer 7 [FIG. 5 (b)]. Next, using the photoresist 10 as a mask, a part of the current confinement layer 7 is removed by etching using a phosphoric acid-based etching solution [FIG. 5 (c)]. Then, after removing the photoresist 10, the third cladding layer 5 is again formed by the MOCVD method.
(P-type Al _0.5 Ga _0.5 As, carrier concentration 5 × 10 ¹⁷
/ Cm ³ , thickness 0.5 μm, contact layer 6 (p-type G
aAs, carrier concentration 1 × 10 ¹⁹ / cm ³ , thickness 3 μm
m) is grown [FIG. 5 (d)].

After that, an upper electrode (not shown) on the p-side,
By forming the n-side lower electrode 9 and cleaving the wafer into chips, a semiconductor laser device having the structure shown in FIG. 4 can be obtained.

[0006]

However, the semiconductor laser device manufactured as described above has the following problems. It is the MOCV again in the process of FIG.
When the third clad layer 5 is grown by the D method, since the wafer has once been placed in the atmosphere until then, the surface of the second clad layer 4 has been oxidized and the third clad layer 4 to be grown on top of this has been oxidized. This is because the crystallinity of the clad layer 5 is deteriorated and a good quality crystal cannot be obtained. If an oxide film is present on the surface of the second cladding layer 4, when the semiconductor laser device is oscillated, the resistance of the region of the oxide film is increased, so that the oscillation threshold current is increased and the injection current is changed to light. The differential efficiency of conversion is also reduced.

The present invention has been made in view of the above points, and an object thereof is to grow a third clad layer without oxidizing the surface of the second clad layer and obtain good crystallinity thereof. Accordingly, a method of manufacturing a semiconductor laser device having improved characteristics is provided.

[0008]

In order to solve the above problems, the method of the present invention comprises a first cladding layer, an active layer, a second cladding layer and a current confinement layer on one main surface of a GaAs substrate. After sequentially forming and patterning the current confinement layer, when etching a part of the current confinement layer, the current confinement layer at a portion corresponding to the light emitting region of the active layer is left thin to about 0.05 μm, and then the third current confinement layer is formed. Before forming the clad layer, the AsH ₃ partial pressure is 5 × 10 ⁻⁵ to 1 × in the AsH ₃ atmosphere in this state.
A heat treatment at 900 to 1050 ° C. is performed under 10 ⁻³ to evaporate the thin layer of the current confinement layer that reaches the second cladding layer.

[0009]

As described above, the method of the present invention evaporates the thin layer of the current confinement layer in the MOCVD apparatus before forming the third cladding layer, and the second layer is formed until the evaporation is completed.
Since the surface of the clad layer is covered with the current confinement layer and the third clad layer and the contact layer can be continuously grown, there is no room for forming an oxide film on the surface of the second clad layer. The manufactured semiconductor laser device has low threshold current and high differential efficiency.

[0010]

EXAMPLES The present invention will be described below based on examples. The structure of the semiconductor laser device obtained by the method of the present invention is
Since the manufacturing process is basically the same as that shown in FIG. 4 and only a part of the manufacturing process shown in FIG. 5C is different, here, FIG.
Illustration of the steps corresponding to (b) and (d) is omitted, and only the points different from the conventional one will be illustrated.

FIG. 1 is a schematic cross-sectional view for explaining the method of the present invention as an improvement of the process shown in FIG. 5 (c), and the same reference numerals are used for the same parts as in FIGS. 4 and 5. is there. Figure 1 Figure 5 (c) differs from the can using a phosphoric acid etchant, the portion of the current confinement layer 7 during etching removal is to leave a thin layer 7a in the current confinement layer 7 . That is, in the present invention, after the step of FIG. 5B, the active layer 3 corresponding to the light emitting region is formed by using a phosphoric acid-based etching solution.
Etching is performed so as to form the thin layer 7a while leaving the upper current confinement layer 7 at about 0.05 μm. This can be easily achieved by setting the etching time to about 9/10 in the case of FIG.

Next, after removing the photoresist 10 used for patterning, the MOC is performed while leaving the thin layer 7a.
After being placed in a VD apparatus, heat treatment is performed at 900 ° C. for 60 minutes in an arsine atmosphere with a partial pressure of AsH _{3 of} 3 × 10 ⁻⁴ . By doing so, the thin layer 7a remaining in the current confinement layer 7 is evaporated by the heat treatment, and the clean surface of the second cladding layer 4 appears.

At this time, G of the thin layer 7a of the current confinement layer 7
The evaporation rate of aAs and AlGaAs of the second cladding layer 4 is much smaller in AlGaAs than in GaAs, and AlGaAs is 1/100 or less of GaAs. Therefore, when the surface of the second cladding layer 4 appears. Thin layer 7a
Evaporation of stops automatically. Here, the results of studying the temperature dependence on the evaporation rate of the thin layer 7a and the evaporation rate dependence on the AsH ₃ partial pressure will be described. First, the evaporation temperature was changed, the processing time was 60 minutes, the AsH ₃ partial pressure was 3 × 10 ⁻⁴ , and the evaporation rate was calculated using a surface roughness meter. The results are shown in FIG. Shown in.
From FIG. 2, it is understood that when the evaporation temperature is 850 ° C., evaporation hardly occurs. This is the same even if the AsH ₃ partial pressure is changed. Further, when the evaporation temperature is set to 1100 ° C., As is evaporated from the surface and the surface condition deteriorates. Comparing the characteristics of the obtained semiconductor laser devices, the oscillation threshold current is higher when the evaporation temperature is 1100 ° C. than when the evaporation temperature is 900 ° C. This is because the dopant was diffused by the high temperature heat treatment, and in order to prevent this, the upper limit temperature is preferably set to 1050 ° C. From these facts, the evaporation temperature is appropriately in the range of 900 to 1050 ° C.

Next, AsH₃Changing the partial pressure, the processing time is 60
Min, evaporation temperature is set to 900 ° C, and evaporation is performed using a surface roughness meter.
The result of speed calculation is AsH in Fig. 3.₃Partial pressure-evaporation rate
It is shown in the diagram. AsH vaporizing from Figure 3₃1 × partial pressure
10^-3From the above, it can be seen that almost no evaporation occurs.
This is AsH₃The partial pressure is too high, and A in GaAs on the surface
This is because s hardly evaporates. Also, AsH₃Minute
Pressure 5 × 10^-FiveAs below, the evaporation of As from the surface
The surface condition deteriorates. Semiconductor that got this
When comparing the characteristics of laser elements, AsH₃3 × 1 partial pressure
0^-FourCompared with the one, the oscillation threshold current rises,
The conversion efficiency is also poor. This is due to the deterioration of the surface condition.
This is because the crystallinity of the grown third clad layer 5 also deteriorates.
It From these results, the thin layer 7a of the current constriction layer 7 was vaporized.
AsH to emit₃Partial pressure is 5 × 10 ^-Five~ 1 x 10^-3Range of
Is appropriate.

Returning to FIG. 1 again, after that, the growth temperature of the third cladding layer 5 is set to 750 ° C.
By forming the contact layer 6 after epitaxially growing the clad layer 5, the same structure as that shown in FIG. 5D can be obtained. As described above, with respect to the semiconductor laser device obtained by the method of the present invention and each several tens of semiconductor laser devices produced by the conventional method,
The oscillation threshold current and the differential efficiency were compared by the average value.
As a result, in the conventional method, the oscillation threshold current was 48 mA, whereas in the semiconductor laser device using the method of the present invention, it was 43 mA, and according to the present invention, the oscillation threshold current was about 10%. Could be reduced. The differential efficiency was 0.34 A / W for the device using the conventional method, whereas it was 0.39 A / W for the device using the method of the present invention, which was an increase of almost 15%. These effects are due to the fact that the method of the present invention prevents the formation of an oxide film on the surface of the second cladding layer 4.

[0016]

In the current confinement type semiconductor laser device, a part of the current confinement layer is etched in the manufacturing process to form the third cladding layer and the contact layer. At that time, the current confinement layer is taken out from the MOCVD apparatus. Since the wafer is placed in the atmosphere, the exposed surface of the second clad layer is oxidized, impairing the crystallinity of the third clad layer and deteriorating the characteristics of the device. On the other hand, according to the method of the present invention, when a part of the current confinement layer is etched, the part corresponding to the light emitting region is left thin and is directly loaded into the MOCVD apparatus as described in the embodiment, and the low voltage AsH is used. _After heat-treating in ₃ atmosphere to evaporate the thin portion of the current confinement layer, continue to the 3rd
Since the clad layer and the contact layer are formed,
The surface of the second clad layer is not exposed to the atmosphere, and therefore no inconvenience caused by the surface oxide film of the second clad layer occurs. As a result, in the semiconductor laser device manufactured by the method of the present invention, the oscillation threshold current is reduced, the differential efficiency is high, and the device characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one step in the method of the present invention.

FIG. 2 is an evaporation temperature-evaporation velocity diagram of a current confinement layer (thin layer).

FIG. 3 AsH ₃ partial pressure-evaporation rate diagram of current confinement layer (thin layer)

FIG. 4 is a schematic cross-sectional view showing a main structure of a semiconductor laser device.

FIG. 5 shows a main manufacturing process diagram of a semiconductor laser device,
(A) is a state in which layers constituting the device are laminated, (b) is a state in which stripes are formed on the current constriction layer, (c) is a state in which a part of the current constriction layer is etched, and (d) is a third clad. Layer and contact layer formed

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 First clad layer 3 Active layer 4 Second clad layer 5 Third clad layer 6 Contact layer 7 Current constriction layer 7 Current constriction layer 7a Thin layer 8 Upper electrode 9 Lower electrode 10 Photoresist

Claims (4)

[Claims] 1. Al _X Ga _1-X As _first layer on a GaAs substrate.
Cladding layer, Al _Y Ga _1-Y As active layer, Al _X Ga
_{A 1-X} As second clad layer, an Al _X Ga _1-X As third clad layer (0 ≦ Y ≦ X ≦ 1), and a GaAs contact layer, and a third clad on both side surfaces of the third clad layer. A method for manufacturing a semiconductor laser device, in which a current confinement layer having a conductivity type opposite to that of a layer is embedded in a direction parallel to a laser light emitting direction, wherein a first clad layer, an active layer, After forming the second cladding layer and the current confinement layer in this order and patterning the current confinement layer, when etching a part of the current confinement layer, the current confinement layer corresponding to the light emitting region of the active layer is left thin. And then heat-treating in an AsH ₃ atmosphere prior to forming the third clad layer, and evaporating the thin layer of the current confinement layer until reaching the second clad layer. 2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the thickness of the layer of the current confinement layer to be left thin is 0.05 μm. 3. A method of manufacturing a semiconductor laser device according to claim 1, wherein the evaporation temperature is 900 to 1050 ° C. 4. The method according to claim 1, wherein A
A method for manufacturing a semiconductor laser device, wherein the sH ₃ partial pressure is 5 × 10 ⁻⁵ to 1 × 10 ⁻³ .