JPH0311688A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To simplify a process by a method wherein a p-type clad layer, an active layer, an n-type clad layer and an n-type cap layer which have been formed on a p-type substrate are etched and a compound semiconductor is grown on both sides of a remaining stripe part in order to form a semiinsulating layer as a current-blocking layer. CONSTITUTION:A p-type clad layer 22, an active layer 23, an n-type clad layer 24 and an n-type cap layer 25 are formed one after another on a p-type substrate 21; these formed layers are etched to be a stripe shape; after that, a semiinsulating layer 28 as a current-blocking layer is formed on both sides of the remaining stripe part. When the semiinsulating layer 28 is formed of a compound semiconductor containing a semiinsulating dopant, the compound semiconductor is doped simultaneously with an n-type dopant. Thereby, it is easy to form an ohmic contact, to omit a process and to reduce an element capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor laser that operates at high output, oscillates at a low threshold, and is capable of high-speed modulation.

(Prior Art) Conventionally, as a manufacturing method of this type of semiconductor laser, the above-mentioned method 1. There is something disclosed in the second document, which will be explained next using FIG.

1st document: Spring 1985 Proceedings of the 32nd Applied Physics Association Conference 126 pages 29P B-6 2nd document: 1985 Autumn 46th Japan Society of Applied Physics Academic Conference Proceedings 206 pages 2P-N 1 First As shown in Figure 2 (al), an n-InP n-type cladding layer 2, a GaInAsP active layer 3,
．． I) Grow InP cladding layer 4. Next, using normal photolithography and chemical etching techniques, the process shown in Figure 2 (
As shown in b), the grown layer is etched using the Sin film 5 as an etching mask, and the width of the layer is etched in the (011) direction.
A mesa stripe portion 6 of 1 to 2 ttm is formed. Next, in the second crystal growth, a p-1nP current blocking layer 7 and an n-1nP current blocking layer 8 are formed on both sides of the mesa stripe section 60, as shown in FIG. 2(C).

After further removing the 5i02 film 5, a p-1nP second cladding layer 9 and a p-GarnAsP cap layer 10 are grown in the third crystal growth as shown in FIG. 2Fdl to complete the basic structure of the semiconductor laser. . After that, after forming electrodes on the substrate 1 side and the cap layer 10 side, the width 1lIo = 250 to 350 pm, the resonator length L = 250
~350pm (Wo, L is shown in Figure 2 (b))
Each laser element is completed by folding it to a size of . When this element is operated by applying an appropriate bias,
The cross-marked portion shown in FIG. 2(d) becomes a reverse bias, and current effectively flows through the active layer 3 portion, allowing low threshold oscillation and high output operation. This device is disclosed in the above-mentioned first document.

In order to improve high-speed modulation characteristics, it is effective to reduce the capacitance of the element. However, in the above device structure, the current blocking layers 8 and 9 are reverse biased, and a large capacitance exists due to the expansion of the depletion layer formed there. Therefore, usually the second
The manufacturing method shown in Figure 1 (disclosed in the second document) is the second
The basic structure shown in Figure fd) is taken after manufacture. That is, there is a gap of 1' on both sides of the mesa stripe section 6 including the active layer 3.
2 grooves 11 so that +2 is 20-30 am (deep enough to reach substrate 1, width generally 10-20 pm)
form. Thereafter, a SiO□ film 12 is formed on the entire surface of the cap layer 10 including the groove, and after a striped window 13 for electrode contact is opened in the upper part of the active layer 3, an electrode 14 is formed. According to this method, the current blocking layer 8
．． The reverse bias portion 9 (marked with a cross) is only the inner width W2 portion of the two grooves 11, and the area of the reverse bias portion is approximately 1710, so the capacitance is also approximately 1710.

Therefore, it becomes an element capable of high-speed modulation.

(Problems to be Solved by the Invention) However, in the conventional manufacturing method as described above, the two grooves 11 are dug after the basic structure of the semiconductor laser is formed, which increases the number of manufacturing steps, and also requires additional steps such as electrode formation. There is a problem that increases the number of difficult processes.

Moreover, even if the portion becomes reverse biased, it always exists even if it is reduced, so it is difficult to make the capacitance smaller and perform faster modulation operation. Furthermore, since an n-type substrate is used as the substrate 1, the conductivity type of the cap layer 10 portion is p-type, and the p-type layer is used to form an ohmic contact when forming an electrode with a narrow window structure as in this structure. is difficult,
The series resistance of the element tends to be high. For this reason, when a large amount of current is passed through, there is a problem that the amount of heat generated increases and the high output characteristics are impaired.

This invention solves the above-mentioned problems, namely: (1) The manufacturing process is numerous and complicated; (2) The element capacitance cannot be made smaller; (2) It is difficult to form an ohmic contact and the series resistance becomes high, making it difficult to obtain high output characteristics. cannot,
It is an object of the present invention to provide a method for manufacturing a semiconductor laser which can easily obtain a high-performance semiconductor laser by eliminating this problem.

(Means for Solving the Problems) In this invention, an n-type substrate is used. In addition, on the n-type substrate, a p-type laser I'1m, an active layer, an n-type cladding layer, an n
After sequentially forming a mold cap layer and etching the formed layer into stripes, semi-insulating layers are formed as current protection layers on both sides of the remaining stripes. Moreover,
When this semi-insulating layer is formed of a compound semiconductor containing a semi-insulating dopant, the compound semiconductor is doped with an n-type dopant at the same time.

(Function) If an n-type substrate is used, it can be used as a cap layer above the active layer.
An n-type cap layer can be formed with which ohmic contact can easily be formed between the n-type cap layer and the electrode thereon.

Also, if a semi-insulating layer is formed as a current blocking layer,
Since the device capacitance due to the reverse bias portion in the current blocking layer portion is eliminated, the device capacitance can be minimized by omitting complicated steps such as forming two grooves and forming striped contact windows.

Furthermore, when forming this semi-insulating layer with a compound semiconductor containing a semi-insulating dopant, for example, a Fe-1nP layer, n
When a type substrate is used, the p-type impurity is Fe-1 from the substrate.
Solid phase diffusion may occur in the nP layer.

Then, the conductivity type of the bank ground of the InP layer (the conductivity type in the undoped state) is reversed from the low concentration n-type to the p-type, so even if doped with Fe, which is a semi-insulating dopant, semi-insulating property cannot be obtained. I can't do it.

On the other hand, according to the present invention, the semi-insulating 1゛-
Since the compound semiconductor (InP layer) is doped with an n-type dopant such as Se or S along with Fe in the punt, even if there is solid-phase diffusion of p-type impurities from the substrate, the InP
The conductivity type of the bank ground of the layer is maintained at a low concentration n-type, and a semi-insulating layer having a stable high specific resistance is formed by doping with Pe.

(Example) An embodiment of the present invention will be described below with reference to FIG.

Although this embodiment concerns an ordinary Fabry-Perot type laser, the present invention can also be applied to a distributed feedback type laser including a diffraction grating in the active layer portion.

First, as shown in FIG.
P active layer 23 n-InP cladding layer 24 and n-Ga
An InAsP cap layer 25 is sequentially grown.

Next, as shown in FIG. 1 (bl), a SiO□ film pattern 26 is formed on the cap Ji 25, and the active layer width is cut using this SiO□ film pattern 26 as an etching mask.

By etching the grown layer so that the value becomes 1 to 'l prn, a mesa-shaped stripe @27 made of the remaining grown layer is formed.

Next, using the SiO□ film pattern 26 as a mask, a semi-insulating layer 28 is selectively grown on both sides of the mesa stripe portion 270 to approximately the same height as shown in FIG. 1 (C1). 27 is buried in a semi-insulating layer 28. Here, the semi-insulating layer 28 can generally be formed by doping a transition metal having a depth unit as an impurity and growing a compound semiconductor. In this example, metal organic vapor phase epitaxy (Metal
organic Vapor Phase Epitax
A high-resistance semi-insulating layer 28 is obtained by growing an InP layer by introducing Fe as an impurity using MOVPE. In this case, the conductivity type of the bank ground of the InP layer must be n type and the impurity concentration must be low. The impurity concentration is, for example, IXIO16 cm-' or less. In other words, doping with Fe at a concentration higher than this impurity concentration results in high resistance.

However, when the p-type substrate 21 is used as described above, the p-type impurity Zn doped in the substrate 2I is
e Solid phase diffusion may occur during the growth of the InP layer.

As a result, the conductivity type of the background of the InP layer becomes p-type, and semi-insulating properties cannot be obtained by doping with Fe. Therefore, in order to keep the conductivity type of the bank ground of the InP layer to n-type with a low impurity concentration, in this embodiment, P
In addition to e, the InP layer is doped with n-type dopant Se or S. As a result, a semi-insulating layer 28 having a stable and high specific resistance is obtained.

After forming the semi-insulating layer 28 in this way and filling the stripe portion 27, after removing the 5iOz film pattern 26, as shown in FIG.
An n-side electrode 29 is formed on the sP cap layer 25 and the semi-insulating layer 28, and a p-side electrode 30 is further formed on the back surface of the substrate 21. Thereafter, the laser device is completed by folding the material to a predetermined size.

(Effect of the invention) As explained in detail above, according to the method of this invention,
Since a p-type substrate is used as the substrate, an n-type cap layer with which ohmic contact can be easily formed between the active layer and the electrode can be formed as a cap layer above the active layer. According to the n-type cap layer, it is possible to form an ohmic contact with the electrode as described above, thereby lowering the series resistance of the element.
You can expect high output. Further, according to the method of this invention,
A semi-insulating layer is formed as the current blocking layer, and since the semi-insulating layer eliminates the element capacitance due to the reverse bias portion in the current blocking layer, it is possible to form two grooves or a striped contact window. By omitting complicated and multi-step processes such as the above, the element capacitance can be minimized, and a laser element capable of high-speed modulation can be obtained. Moreover, in the method of the present invention, when forming the semi-insulating layer as the current blocking layer, an n-type dopant is introduced together with a semi-insulating dopant to grow a compound semiconductor, so that p Even if there is in-phase diffusion of type impurities, a semi-insulating layer with high resistivity can be stably formed.

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing an embodiment of the semiconductor laser manufacturing method of the present invention, and FIG. 2 is a process sectional view showing a conventional semiconductor laser manufacturing method. 21...p-1nP substrate, 22...p-InPn
Waku5fu, 23-GaInA5P active layer, 24- n-
InPn layer 5, 25... n-GaInAsP cap layer, 27... mesa-shaped stripe portion, 28... semi-insulating layer. (C) Kuchikacho JP-A-3 11688 (5) Conventional manufacturing method

Claims (1)

[Claims] A step of sequentially forming a p-type cladding layer, an active layer, an n-type cladding layer, and an n-type cap layer on a p-type substrate, a step of etching the formed layers into stripes, and a step of etching the formed layers into stripes, and the remaining stripes. A method for manufacturing a semiconductor laser comprising the steps of: growing a compound semiconductor containing an n-type dopant together with a semi-insulating dopant on both sides of the region to form a semi-insulating layer as a current blocking layer.