JPS59155977A - Manufacture of semiconductor laser element - Google Patents

Abstract

PURPOSE:To assure stable operation even at high optical output with low oscillating threshold current by a method wherein a formed layer of double hetero construction is removed by etching process to form a transparent semiconductor layer into the removed space further forming a reflecting surface on the semiconductor layer. CONSTITUTION:The first clad layer 2, a laser active layer 3, the second clad layer 4 and a cap layer 5 are formed on a semiconductor substrate 1. Firstly the layer comprising the layers 2-5 is removed by chemical etching process until the layer 1 is exposed. Secondly a transparent semiconductor layer 6 is formed into the space removed by the etching process. Lastly the layer 6 is removed by reactive ion etching process to form a reflecting surface 7 of a laser resonator. The semiconductor laser element manufactured by the procedures so far mentioned may be assured of stable operation even at high optical output since its optical output end is constructed to be hardly deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing a semiconductor laser device.

[Prior art]

Among the deterioration phenomena caused by the optical output of a semiconductor laser element, the most important is the deterioration of the optical output end face. Regarding the phenomenon in which the optical output end face of a semiconductor laser element is instantaneously destroyed when the optical output becomes high, by making the vicinity of the optical output end face transparent to the laser's oscillation wavelength, the destruction limit output can be significantly increased. It is known that it will happen. (For example, High optical power dens
ity emission from a ”wind
ow-stripe” Ajl' GaAs doub
le-heterostructure 1aser;
H-Yones, et, at; Appl.

Phys, Let:t, Vol, 34N6.15
(1979) 637p- and GaAs-AJ G
a As D, H, La5ers with Bur
ied Facet; H,5ai-to,et,a
l, ; J, J, A, P, Vol, 17 No,
5 (1978) 865 p.) One method of making the vicinity of the light output end face transparent is to embed a transparent semiconductor crystal in the area near the light output end face and cleave it in this region to make the laser reflective surface. The method of making was implemented.

According to such conventional methods, the precision of cleavage is poor, so it is necessary to increase the length of the transparent semiconductor region in advance. However, since the light is dispersed while propagating through the transparent semiconductor region, as the length of the transparent semiconductor region increases, the efficiency with which the light is reflected by the light output end face and recombined with the active layer becomes relatively small. . Therefore, the conventional semiconductor laser device of this type has a disadvantage in that the oscillation threshold current value becomes relatively large.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing a semiconductor laser device that operates stably up to a high optical output with a low oscillation threshold current value.

[Summary of the invention]

In order to achieve the above object, the method for manufacturing and using a semiconductor laser device according to the present invention is to manufacture a semiconductor laser device through the following steps. A double heterostructure crystal consisting of a first cladding layer, a laser active layer, and a second cladding layer is formed on a semiconductor substrate, and a region of the formed layer near the optical output end face of the laser element is deeper than the laser active layer. Etch to the desired location and remove. This etching is performed by a chemical etching method or a method using a combination of a reactive ion etching method and a chemical etching method, taking into consideration damage to the laser active layer. In this way, a semiconductor layer that is transparent to the laser wavelength is formed in the part where the double heterostructure formation layer is removed, and a part of this transparent semiconductor layer is processed to be deeper than the plane that extends the laser active layer. The reflective surface is formed by etching the surface so that the surface is substantially perpendicular to the plane of the laser active layer. For etching, a reactive ion etching method in which the sides of the processed portion are made almost vertical is suitable for creating a reflective surface, or chemical etching may be used as long as the shape can be controlled. In the method of creating a reflective surface on a double heterostructure by direct reactive ion etching, the processing may create crystal defects in the laser active region, which may adversely affect the lifetime characteristics of the laser element, and the etching rate may be reduced. If the etching speed differs depending on the crystal orientation or the laser active layer and the cladding layer, there is a problem that it is difficult to make the machined surface perpendicular to the cavity length direction. A crystal with a terrorist structure (this uses a chemical etching method that has little effect on the laser active layer, and the reflective surface of the transparent 16 conductor layer is etched with a uniform crystal in the non-excited region away from the laser active layer). Therefore, it is possible to form a smooth irregular surface perpendicular to the plane of the laser active layer with little adverse effect on the life of the laser element.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. .

FIG. 1 is a cross-sectional view in a direction parallel to the direction of propagation of light, showing an embodiment of a semicircular semiconductor laser device manufactured by the method of manufacturing a semiconductor laser device according to the present invention, and FIG. Fig. 3 is a cross-sectional view taken in a direction perpendicular to the direction of movement of the conductive laser element.
The figure shows an example of a change in the laser oscillation threshold current value when the length of the transparent semiconductor layer in the resonator length direction is changed in the semiconductor laser device. In this embodiment shown in FIGS. 1 and 2, an n-type GaAs substrate (Si doped, n-
A groove with a width of about 4 μm and a depth of about 1.3 μm is formed in the [011] direction on the 1 The width is about 0 on the vertical side of the groove.
3μm) 2, undoped Ga0.86AJ0.14A
s laser active layer (thickness approximately 0.06 μm) 3. p-type Ga, ), 5. Ago5As cladding layer (Zn doped,
pm2×1017cm-3-, thickness approximately 2.3 μm)
4, p-type GaAs cap layer (Ge tope, n-1
x 1018 cm-3, thickness approximately 0.6 pm) 5 was continuously formed by a liquid phase growth method. Finally, a double heterostructure of n-type GaO, 5Al formed as shown above.
o,5 As cladding layer 2, undoped Ga0.86
Aj? o, I4 As laser active layer 3, p-type Gao5A
lo5As cladding layer 4, p-type GaAs capping layer 5
A grown layer of 250 μm was left in the cavity length direction, and the remaining end portions were removed by chemical etching using a sulfuric acid-hydrogen peroxide based etching solution until the n-type GaAs substrate 1 was exposed. Etching mask (Koha Plasma C
A silicon nitride film formed by VD was used. Undoped G is applied again to the part from which the growth layer has been removed by liquid phase growth.
aO,75,”0.25 After forming the As transparent layer 6,
Ant'-pu Gao by reactive ion etching,
The transparent semiconductor layer 6, which is a 75Azo, 25As transparent layer, was etched to form the irregular surface 7 of the laser resonator. At this time, the length of the transparent semiconductor layer 6, that is, the length in the cavity length direction, was approximately 3 μm. Next, a silicon nitride film 8 is formed on the surface, and a current confinement insulating film having a striped opening with a width of about 4 μm is provided above the laser active region.
c7) A p-side electrode 9 and an n-side electrode 1° of Au-Ge-Ni were formed by vacuum evaporation. After completing the two wafer processing steps, a semiconductor laser chip was cut out by scribing and fixed on a heat sink.

The semiconductor laser device of this example oscillated at a wavelength of 780 nm and a threshold current value of about 5 QmA. Figure 3 shows an example of the current vs. optical output characteristics of this embodiment.As shown by the dotted line in the figure, a conventional semiconductor laser device in which the active layer is continuous up to the optical output end face does not emit light during high optical output operation. Although the output end face is often destroyed and deteriorated, the semiconductor laser device of this example has a structure in which the optical output end face is not easily deteriorated, so stable operation was obtained even at high optical output as shown by the solid line in the figure. Furthermore, in this embodiment, if the length of the transparent semiconductor layer 6 in the cavity length direction is increased, the oscillation threshold current value of the laser element increases.
As shown in FIG. 4, if the length of the transparent semiconductor layer 6 in the cavity length direction is set to 5 μm or less, the oscillation threshold current value hardly increases and the increase value is 20% or less. The semiconductor laser device of this example was operated continuously at an optical output of 40 mW and an ambient temperature of 70° C., and almost no deterioration was observed even after 1000 hours.

FIG. 5 is a cross-sectional view in a direction parallel to the direction in which light travels, showing another embodiment of a semiconductor laser device manufactured by the method for manufacturing a semiconductor laser device according to the present invention. Striped grooves were formed on the n-type GaAs substrate 1 in the same manner as in the previous embodiment,
n-type ca[+, 5 AzCl, 5 As cladding layer 2,
Undoped Ga0.86 Aj? O, I4 As L/
-f g-type layer 3 p-type Ga(1,5A/(1,5As) cladding layer 4 and p-type GaAs cap layer 5 were successively formed by liquid phase growth method.Next, the tuple heterostructure formed as described above was Each grown layer 2.3.4.5 is left with 250 μm for the laser cavity and 60 μm for the photodetector in the cavity length direction, and the remaining grown layer portion is made of n-type Ga.
The As substrate 1 was removed by chemical etching using a sulfuric acid-hydrogen peroxide based etching solution until it was exposed. The distance between the remaining growth layer for the laser resonator and the growth layer for the photodetector was 30 μm. Finally, the liquid phase growth method (thus, undoped Gao7s A
A 0.25 As transparent layer 6 was formed, and the transparent layer 6 was etched by reactive ion etching to form a refractory surface 11 of a laser resonator and a light incident surface 12 of a photodetector. Thereafter, a current confinement was formed on the upper surface. A silicon nitride film having an opening 1 is formed above the laser active region as an insulating film for the laser resonator p-side electrode (Cr, Au) 9, photodetector upper electrode (Cr, Au) 13, and substrate electrode ( Au-Ge
-Ni) 10 was formed by a vacuum evaporation method. After completing the wafer processing process, scribing was performed to cut out laser chips to manufacture semiconductor laser composite devices. The photodetector section of the semiconductor laser composite device of this example was reverse biased by applying a negative voltage to the upper electrode 3, and was used as a laser light output monitor. The laser resonator section was able to operate stably even at a low oscillation threshold current value and high optical output, as in the previous example.

The method for manufacturing a semiconductor laser device according to the present invention is applicable not only to the Ga Az As-based semiconductor laser device shown in each of the above embodiments, but also to an InGaAsF-based semiconductor laser device, such as an InGaAsF-based semiconductor laser device, which is a group V compound semiconductor. be able to.

〔Effect of the invention〕

As described above, the method for manufacturing a semiconductor laser device according to the present invention involves the method of manufacturing a semiconductor laser device by forming a light output end face of the laser device (either by providing a transparent semiconductor layer to cover the light output end face to prevent deterioration of the light output end face at the time of high light output, or by covering the light output end face with the transparent semiconductor layer). Unlike the conventional method of cleavage, the formation of the reflective surface at the light output end face of the layer is performed by etching a uniform crystal separated from the laser active layer, so the length of the transparent semiconductor layer in the cavity length direction is Since it can be controlled almost within the processing precision of photolithography and etching, it can be made very short to 1 to 5 μm, and it is also possible to obtain a smooth reflective surface, so the loss of light propagating between this is extremely small. Therefore, it is possible to obtain a semiconductor laser device that has a small oscillation threshold current value and operates stably even at high optical output.Furthermore, etching is used instead of the cleavage method to form the irregular surface of the transparent semiconductor layer. This is also advantageous in the process of integrating a laser element and an electric circuit.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of a semiconductor laser device manufactured by the method of manufacturing a semiconductor laser device according to the present invention. The figure is a cross-sectional view in the direction perpendicular to the direction of light propagation, Figure 3 is a diagram showing an example of the current-light output characteristics of the semiconductor laser element described above, and Figure 4 is the resonance of the transparent semiconductor layer in the semiconductor laser element mentioned above. A diagram showing an example of a change in the laser oscillation threshold current value when the length in the longitudinal direction is changed, and FIG. 5 shows another example of a semiconductor laser device manufactured by the method for manufacturing a semiconductor laser device according to the present invention. FIG. 3 is a cross-sectional view taken in a direction parallel to the traveling direction of the light shown in FIG. ] ... Semiconductor substrate 2 ... First cladding layer 3 ... Laser active layer 4 ... Second cladding layer 6 ... Transparent semiconductor layer 7 ... Reflective surface Patent attorney Junnosuke Nakamura t] Figure tJ Figure 2 Figure 3 Figure tJ

Claims (1)

[Claims] (1) A double heterostructure consisting of a first cladding layer, a laser active layer, and a second cladding layer is formed on a semiconductor substrate, and a part of the growth layer of the tuple heterostructure is chemically etched or reactive ion etched and chemically etched. When used in combination with etching, it can be removed to a deeper position than the laser active layer.
- A semiconductor layer that is transparent to the laser wavelength is formed in the area where the growth layer has been removed, and a part of this transparent semiconductor layer is activated by laser so that the processed surface is approximately perpendicular to the plane of the laser active layer. A method of manufacturing a semiconductor laser device in which a nonconforming surface is formed by etching to a deeper position than the layer. (2) The method for manufacturing a semiconductor laser device as described in claim 1, wherein the length of the transparent semiconductor layer in the cavity length direction is 1 to 5 μm.