JPH03283693A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To correctly control width of a ridge and thickness of a clad layer to improve manufacturing yield and device characteristics by forming a stripe ridge by means of selective growth. CONSTITUTION:An n-In0.5(Ga0.3Al0.7)0.5P clad layer 11, an In0.5Ga0.5P active layer 12 and a p-In0.5(Ga0.3Al0.7)0.5P clad layer 13 are formed on an N-GaAs substrate 10. A mask 19 having a stripe opening is formed on the layer 13. A p-In0.5(Ga0.3Al0.7)0.5P layer is selectively grown on an exposed part of the layer 13 to form a stripe p-InGaAlP ridge 14. A p-In0.5Ga0.5P easily-power- supplied layer 15 is formed on it. After the mask is removed, a p-GaAs contact layer 16 is formed. A p-side electrode 17 is formed on the layer 16 while an n-side electrode is formed on the substrate 10 side to obtain HBB semiconductor laser.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser used as a light source for optical information processing, optical measurement, etc. This invention relates to a laser manufacturing method.

(Prior art) In recent years, color semiconductor lasers using InGaAIP materials with an oscillation wavelength in the 0.6 μl band have been commercialized, and are used in high-density disk devices, light sources for laser beam printers, barcode readers, optical measuring instruments, etc. It is expected to be used as a light source.

For such applications, it is necessary to focus the laser beam into a minute spot, and it is important that the laser beam has stable transverse mode oscillation and a small astigmatism difference.

In order to achieve the above characteristics, it is necessary to use a refractive index guided transverse mode control semiconductor laser. As shown in FIG. 4, this type of laser uses an InGaAIP material and has a distripe structure in the color of the InGaAIP material.
A semiconductor laser with a Hatcro barrier blocking) structure has been proposed (Kazuhiko
ILnya Qtal Extend At) Str
aetSof rhc 20th Conference
e on 5o11d 5tate Dlvlces
and Materials, Tokyo, 198
8. P2O3-110).

To manufacture this semiconductor laser, first, as shown in Fig. 4(a).
l: As shown, n-1nGa on the n-GaAs substrate 30
AIP cladding layer 31, 1nGaP active layer 32. p-1
After forming the nGaAIP cladding layer 33 and the p-1nGaP conductive layer 35 in sequence, the portion where the ridge is to be formed is masked with a 5i02 film 39. Next, Fig. 4 (b
), selectively etching a part of the conductive layer 35 and the cladding layer 33 by wet etching,
Form a ridge stripe. Next, 5in2 membrane 39
After that, as shown in FIG. 4<C>, a p-1caAs contact layer 36 is grown to cover the ridge stripe, and a p-side electrode 37 and an n-side electrode 38 are further formed.

In the semiconductor laser obtained in this way, p-
Since there is a high heterobarrier at the junction between the 1nGaAIP cladding layer 33 and the p-GaAs buried contact layer 36, it is difficult for current to flow. However, p-1nG at this junction
By providing the aP current conduction facilitation layer 35, p-GaA
s contact layer 36 and p-1nGaAIP cladding layer 3
The height of the heterobarrier existing at the junction with No. 3 can be lowered, allowing current to flow more efficiently.

In other words, in this HBB semiconductor laser, since the p-InGaP current conducting layer 35 is formed in at least a part of the ridge portion, the p-InGaAIP cladding layer 35 is formed on at least a part of the ridge portion.
No current flows through the junction between 3 and the p-GaAs layer 36;
Current confinement is achieved by allowing current to flow only through the portion of the ridge portion having the p-1nGaP current-carrying layer 35.

Furthermore, by decreasing the ridge stripe width W and the distance @h between the pGaAs contact layer 36 and the InGaP active layer 32, radiation characteristics with a small astigmatism difference of less than 10μ and a small beam aspect ratio, which are useful for application to optical disks, can be obtained. A fundamental transverse mode oscillation is obtained.

However, this type of laser has the following problems. That is, when forming striped ridges,
Since etching is performed using SiO2 as a mask, the width W of the ridge portion cannot be accurately controlled due to under-etching to the bottom of the 5i02 mask.Furthermore, the thickness h of the cladding layer 33 other than the ridge portion is also etched. This is also difficult to control precisely. Moreover, since etching proceeds simultaneously with respect to the width W and thickness h, it is not possible to control both independently, so the control of the astigmatic difference, aspect ratio, and stable transverse mode oscillation described above can be realized with good reproducibility. That was difficult.

Furthermore, when an HBB semiconductor laser is manufactured by the conventional method, the p-1nGaP current carrying layer can only be formed on the upper surface of the ridge, as shown in FIG. For this reason, the internal resistance Rs of the semiconductor laser becomes large, and there is a risk that the device characteristics will deteriorate due to heat generation during operation.

(Problems to be Solved by the Invention) As described above, in the conventional method for manufacturing an HBB structure semiconductor laser, the ridge portion to be formed is masked with a dielectric film such as 5i02, and the ridge structure is formed by wet etching. For this reason, it is difficult to accurately control the thickness h of the cladding layer, which is determined by the etching time of the width W1 of the ridge part, due to underetching of the masked part.
This has been a factor leading to a decline in manufacturing yield and device characteristics. Further, there was a problem in that both the ridge width W and the cladding layer length h could not be independently controlled.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to accurately control the width W of the ridge portion and the thickness h of the cladding layer without using wet etching. An object of the present invention is to provide a method for manufacturing a semiconductor laser that can improve manufacturing yield and device characteristics.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to form the ridges not by etching but by using selective growth.

That is, the present invention provides a method for manufacturing a semiconductor laser having a striped ridge portion, in which In is formed on a compound semiconductor substrate.
After forming a double heterostructure in which a GaAIP-based material layer is sandwiched between cladding layers, a mask having stripe-shaped openings is formed on this double heterostructure, and then exposed through the openings of the mask. A semiconductor crystal layer is grown on the double heterostructure to form a ridge stripe, and then a conductive layer is grown on the ridge stripe, and then the mask is removed and a contact layer is formed to cover the ridge stripe. This is a method that allows the formation of

(Function) In the present invention, the InGaAIP cladding layer on the side opposite to the substrate of the double heterostructure is grown to a desired thickness h. After that, a striped opening with a width W is left at the position where the ridge is to be formed on this cladding layer.
A dielectric film such as i02 is used as a mask, and a semiconductor crystal layer having the same composition as the cladding layer is successively grown thereon.

By appropriately selecting the growth conditions at this time, SiO2
It is possible to selectively grow an InGaAIP layer only on the cladding layer exposed by the stripe groove of width W without growing InGaAIP on the mask.

Further, by utilizing the difference in growth rate between the (111) plane and the (100) plane, a trapezoidal ridge as shown in FIG. 4(b) can be formed. Furthermore, 1nGa
In the growth of P, it does not grow on the (111) plane but on the (100
) by selecting conditions that allow InG to grow.
A current carrying layer such as aP can be formed only on the top surface of the InGaAIP ridge. Furthermore, by selecting different growth conditions, it is also possible to form the InGaPGaP conductive layer so as to cover the entire InGaAIP ridge.

In this way, the thickness h of the cladding layer other than the ridge part is determined by the layer thickness of the first grown f nGaA I P cladding layer, that is, the growth time. Since it is possible to directly control W and h when they are formed on top, the controllability of W and h is much better than when both are controlled by etching. Furthermore, dimensions of W and h can be controlled independently. As a result, stable index-guided fundamental transverse mode oscillation can be realized in the HBB semiconductor laser.

In addition, by controlling W and h by conventional etching, HB
When manufacturing a B semiconductor laser, the InGaPa dielectric layer could only be formed on the top surface of the 1nGaAIP ridge as shown in FIG. 1nGaP on the entire surface of
It is also possible to form a current-carrying layer. by this,
The cross section of the current flowing through the ridge portion increases, the internal resistance Rs decreases, and it becomes possible to suppress heat generation during operation.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing the manufacturing process of an HBB semiconductor laser according to an embodiment of the present invention.

First, as shown in FIG. 1(a), the substrate temperature is maintained at 600 to 800°C, for example 800°C, by low pressure MOCVD, and the m/V ratio is 400. At a pressure of 25 Torr, n-Ga
n-1no, (G
ao,] A 10.7) o, s P cladding layer 11. In(1,s Gao,s
P active layer 12 and p-1no,s with a thickness of 0.2 μm (Gao, i A 1G, 7)
A 0.9 P cladding layer 13 is sequentially grown and formed. At this time, by determining the growth time so that the thickness h of the InGaAIP cladding layer 13 would be a desired value, the thickness h of the cladding layer 1v could be well controlled.

Next, as shown in FIG. 1(b), a cladding layer 131 is formed.
A 5in2 film is deposited by CVD method etc. on the 5in2 film.
The film is removed in stripes having a width W (for example, 5 μm) to form a mask 19 having stripe-shaped openings. In addition,
The mask 19 is not limited to SiO2, and other dielectric films such as SiN may be used.

Next, as shown in FIG. 1(e), by low-pressure MOCVD at a substrate temperature in the range of 800 to 800°C, the width W not grown on the Si mask and not masked with SiO□ is grown.
pI no, s (G ao, s A
10.7) o,s So that the P layer grows selectively,
The substrate temperature and V1m ratio were set so that the growth rate was different between the (ill) plane and the (100) plane, and the striped p-1nGaA I P ridge portion 14 was formed.

The height of the ridge portion 14 was controlled by the growth time. Furthermore, by selecting growth conditions such as substrate temperature and V/m ratio that allow growth on the (100) plane but not on the (111) plane, InG
a p 1 no, q only on the upper surface of the AIP ridge portion 14
A Gao, sp current carrying capacitor layer 15 was formed.

Next, after removing the SiO2 mask 19 by hydrofluoric acid etching, the ridge portion 1 is etched as shown in FIG. 1(d).
A p-GaAs contact layer 16 is grown to a thickness of 3 μm from the upper end of the ridge so as to cover the conduction facilitating layer 15 and the p-GaAs contact layer 16 . Then, by forming ^Zn/Au on the contact layer 16 as the p-side electrode 17 and forming AuGc/Au on the substrate 10 side as the n-side electrode 18, the HBB semiconductor laser is completed.

In the semiconductor laser thus manufactured, the width W of the ridge portion 14 can be directly controlled when forming the 5i02 mask 19 on the cladding layer 13, and the thickness h of the cladding layer 13 other than the ridge portion 14 is initially grown. InGaAIP
The thickness of the cladding layer 13 is determined by the upper 3 layers. For this reason, w, h
It is possible to accurately control both of them, and furthermore, it is possible to independently control the dimensions of W and h. Therefore, an HBB semiconductor laser having a small nasal point difference and a small aspect ratio can be manufactured with high yield and high reproducibility.

FIG. 2 is a process sectional view for explaining another embodiment of the method of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the previously described embodiments in the method of forming the current conduction facilitation layer 15. That is, as shown in FIG. 2(a), similarly to the method of the previous embodiment, the 5i02 mask 19
The p-1nGaAIP ridge portion 14 is formed by selective growth using p-1nGaAIP. Next, by appropriately selecting growth conditions such as growth conditions and V/m ratio, the p-InGaP current conductive layer 16 is changed to p-InGaP as shown in FIG. 2(b).
It is formed to cover the entire surface of the AIP layer 14. After that, the same growth process as in the previous example (the growth temperature was, for example, 700°C) was carried out.
After that, an HBB semiconductor laser was manufactured as shown in FIG. 2(e).

The thus obtained HBB semiconductor laser can not only accurately control W and H as in the previous embodiment, but also has the following advantages. That is, the ridge portion 14
The internal resistance of the device decreases due to the increased cross-sectional area of the operating current in the device. As a result, heat generation during operation can be suppressed, and element reliability can be improved.

Although InGaP is used as the active layer in each of the above-described embodiments, it is also possible to use InGaAIP, which has a lower A1 composition ratio than the cladding layer. Further, the growth method, growth conditions, etc. when forming the ridge portion and the current-carrying layer can be changed as appropriate depending on the specifications. others,
Various modifications can be made without departing from the spirit of the invention.

FIG. 3 is a sectional view for explaining still another embodiment of the present invention. In this embodiment, first, as shown in FIG. 3(a), an n-GaAs substrate 20 was heated to a substrate temperature of 700° C. by low pressure CVD.

m/V ratio 200. Pressure cuff 0 Torr, n Ga
o, ssA 1 g, 45A s cladding layer 21 (n
-I x 10"cm', 1.2 μm) r undoped GaAs active layer 22 (0.06 μm) and p
-G a 6.55A l O, 45A 8 cladding layer 23 (p-5X 10"cm-', 0.2.cz
m) to grow and form. At this time, the thickness of the cladding layer 23 is 0.2 as described above.

Next, as shown in FIG. 3(b), a 5in2 mask 29 is formed leaving a ridge width W (for example, 5 μm). Thereafter, under the same conditions as in the previous example, as shown in FIG.
A 8 layer (p -5x 10"cm'
) is selectively grown to form a ridge stripe 24 with a height of 1 μm.
form. Next, 5in2 was etched by hydrofluoric acid etching.
After removing the mask 29, as shown in FIG. 3(d),
p-GaAs contact layer 26 (p = 1 x 1
000 cm-') is formed 1.5 μm from the top of the ridge, and an n-GaAs current blocking layer 25 (n = 1
x 10"cs-') was grown to a thickness of 0.5 μm. Thereafter, the current blocking layer 25 was etched in stripes to form a current confinement structure.

After that, as shown in Figure 3 (C), ^urn is applied to the p side.
/Au electrode 27 is formed, and an AuGe/Au electrode 2 is formed on the n side.
By forming 8, a transverse mode control type semiconductor laser could be manufactured. In addition, 5 used for selective growth
The in2 mask may be any of the other 19 body membranes. Also, p
Even if a -G a A g substrate is used, a similar transverse mode control power semiconductor laser can be created by reversing the conductivity type of each layer.

[Effects of the Invention] As detailed above, according to the present invention, the ridge portion is formed not by etching but by selective growth. The width W and the thickness h of the cladding layer can be accurately controlled, thereby making it possible to improve the manufacturing yield and device characteristics of the HBB semiconductor laser.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the manufacturing process of a semiconductor laser according to a method according to an embodiment of the present invention, FIG. 2 is a sectional view showing a process for explaining another embodiment of the method according to the present invention, and FIG. FIG. 4 is a cross-sectional view showing a conventional laser manufacturing process. 10-n-GaAs substrate, 11-n-1n a AIP cladding layer,
12--1n aP active layer, 13--p-1n GaAIP cladding layer, 14--p-1n GaAIP ridge portion, 15--p-1n GaP Current conduction facilitation layer, 16...p-GaAs contact layer, 17.18.
...Electrode, 19...5in2 mask.

Claims (1)

[Claims] a step of forming a double heterostructure portion with an active layer sandwiched between cladding layers on a compound semiconductor substrate; a step of forming a mask having stripe-shaped openings on the double heterostructure portion; and a step of exposing through the openings of the mask. a step of growing a semiconductor crystal layer on the double heterostructure portion to form a ridge stripe; and a step of forming a contact layer so as to cover the ridge stripe after removing the mask. Laser manufacturing method.