JPH08153928A - Manufacture of semiconductor laser array - Google Patents

Abstract

PURPOSE: To make the detuning amount of each element equal, and make the oscillation wave amplitude large, by a method wherein a laser active layer is formed by growing an optical guide layer so as to fill a diffraction grating, and performing selective growth on the guide layer, by using a mask for selective growth wherein the mask width is different between adjacent elements. CONSTITUTION: A diffraction grating 2 is formed on an N-type InP substrate 1. An InGaAsP layer 3 is buried in the whole part of the substrate where the diffraction grating 2 is formed, and turned into an optical guide layer. Thereon a mask 4 for selective growth is formed which is to be used for forming an active layer stripe. The mask 4 is so formed that the width is incremented 10μm in 10-40μm range between neighboring active layer stripes. By performing selective growth using the mask 4, the lower side SCH layer is sequentially grown and active layer stripes for 4 channels are formed just above the buried diffraction grating. After that, unnecessary parts 6 and the mask 4 for growth are eliminated, and a current blocking layer 7 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser array, and more particularly to a method for manufacturing a semiconductor laser array for wavelength division multiplexing (WDM) optical communication in which adjacent elements are arranged at equal wavelength intervals.

[0002]

2. Description of the Related Art As a light source for WDM, there is a demand for a semiconductor laser array in which oscillation wavelengths of adjacent elements are arranged at equal intervals. Conventionally, as a method of manufacturing such a laser array, adjacent distributed feedback (D
There has been a method in which the diffraction grating pitch of the FB) or distributed reflection (DBR) laser is slightly changed to produce a laser array in which the oscillation wavelengths slightly differ from each other. However, in this method, since the active layer is the same for all the elements, the amount of detuning of the difference between the oscillation wavelength and the gain peak wavelength differs depending on the adjacent element, and there is a problem that the wavelength can be shifted only up to about 20 nm.

On the other hand, a method using selective growth has been attempted. If selective growth is used, the composition and thickness of an optical guide layer such as a DFB laser can be controlled by a mask pattern, and even if the diffraction grating pitch is constant, the equivalent refractive index can be modulated to give an oscillation wavelength distribution. . For example,
In a four-wave DBR laser array using MOVPE selective growth by Kato et al. 0, 15, 30, 50
By changing the thickness of the optical waveguide layer to μm and modulating the thickness of the optical waveguide layer, a 4-channel DBR laser array in which the oscillation wavelength of 15 nm is shifted at 5 nm intervals is realized.

Also, Tsutsui et al. Have obtained a wavelength tunable width of 10.1 nm at intervals of about 2.5 nm by using the selective growth in the same manner (Spring 1994 41st Lecture Meeting on Applied Physics) No. 29p-K-14). However, in this case, since the MQW active layer is grown simultaneously with the optical guide layer, the composition and thickness of the active layer are also modulated, and the gain peak wavelength and the oscillation wavelength cannot be controlled independently. Therefore, also in this case, it is difficult to control the detuning amount of each element over a wide wavelength range.

[0005]

DISCLOSURE OF THE INVENTION The present invention eliminates the drawbacks of the conventional semiconductor laser array for wavelength-division multiplex light sources and controls the detuning amount of each laser, thereby providing a wide wavelength range over 50 nm. It is to realize a semiconductor laser array capable of covering the oscillation wavelength over a wide range.

[0006]

According to a method of manufacturing a semiconductor laser array of the present invention, in a distributed feedback type or distributed reflection type semiconductor laser formed in an array on a semiconductor substrate, at least pitches of diffraction gratings between adjacent elements. Forming a diffraction grating so that the diffraction gratings are slightly different from each other, a step of growing an optical guide layer made of a second semiconductor different from the substrate so as to fill the diffraction grating, and an element further adjacent thereto. It is characterized by having a step of forming an active layer of a laser by performing selective growth using masks for selective growth having different mask widths.

Further, according to the method of manufacturing a semiconductor laser array of the present invention, in a distributed feedback type or distributed reflection type semiconductor laser formed in an array on a semiconductor substrate, a selective growth mask having a mask width different between at least adjacent elements. By performing selective growth using the above method, a step of forming an active layer of the laser, a step of growing an optical guide layer made of a second semiconductor different from the substrate on the active layer, and a step of further growing the optical guide layer on the optical guide layer. It has both the step of forming a diffraction grating so that the pitch of the diffraction grating is slightly different between adjacent elements and the step of growing a clad layer made of the same kind of semiconductor as the substrate so as to bury the diffraction grating on it. It is characterized by As a semiconductor substrate, n-type or P-type I
nP and GaAs can be used.

[0008]

The principle of the present invention will be described below. The present invention provides a laser array manufacturing method capable of controlling the oscillation wavelength of each element and independently controlling the detuning amount of each element for the purpose of being applied to a WDM light source or the like. is there.

FIG. 3A shows the relationship between the oscillation wavelength of each element and the gain peak wavelength of a WDM laser array manufactured by modulating only the pitch of the diffraction grating using conventional electron beam exposure or the like. Show. In this method, since the active layer structure of each element is the same, the gain peak wavelength is exactly the same for all elements. Therefore, when only the diffraction grating pitch is changed and the wavelength is changed in each element, the detuning amount (difference between the oscillation wavelength and the gain peak wavelength) varies from element to element as shown in the figure. Normally, when the detuning amount exceeds about ± 5 nm, the laser becomes difficult to oscillate any more. Therefore, the wavelength range of the array laser which can be changed by this method is at most about 20 nm.

On the other hand, the wavelength can also be changed by the above-described method using selective growth. In the selective growth, the composition and thickness of the growth layer can be modulated by changing the width of the mask used. Therefore, the composition and the film thickness of the optical guide layer or the active layer can be changed between the adjacent layers by using the selective growth masks having the different mask widths between the adjacent layers, so that the oscillation wavelength can be changed even if the diffraction grating pitch is the same. . However, in this method, as shown in FIG. 3B, the gain peak wavelength is modulated simultaneously with the oscillation wavelength, so that the oscillation wavelength and the detuning amount cannot be controlled independently.

On the other hand, in the method of the present invention in which these two methods are combined, as shown in FIG. 3C, the oscillation wavelength and the detuning amount of each element of the laser array can be controlled independently. It will be possible. That is, in the method of the present invention, the oscillation wavelength is changed by modulation of the diffraction grating pitch by electron beam exposure or the like, and the bandgap control of the active layer by selective growth is performed, so that the relationship between the gain peak wavelength and the oscillation wavelength of each element is entirely changed. Can be made constant with respect to the element.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a diagram showing a method of manufacturing a distributed feedback laser array (four channels in this case) which is a first embodiment of the present invention. First, as shown in FIG. 1A, a pitch between adjacent ones is changed from 202 nm to 2 on an n-type InP substrate 1.
The diffraction grating 2 changing at intervals of 0.4 nm up to 03.2 nm is formed. Such a diffraction grating having a different pitch between adjacent ones can be easily formed by using electron beam exposure. Next, as shown in FIG. 1B, the entire surface of the substrate on which the diffraction grating 2 is formed is covered with an I
The nGaAsP layer 3 is embedded. This layer is 100 nm thick
It becomes a light guide layer in a distributed feedback laser. Further, as shown in FIG. 1B, a selective growth mask (usually using an SiO 2 mask) 4 for forming an active layer stripe is formed on this layer, and in this case, the active masks whose widths are adjacent to each other are formed. A mask is formed between the layer stripes so as to increase from 10 μm to 40 μm every 10 μm (the width of this mask may be different depending on the growth apparatus and growth conditions). By selectively growing using such a mask, the lower SCH layer is sequentially grown, and FIG.
(C) As shown in FIG.
Active layer stripes 5 for channels are formed. At this time, since unnecessary portions 6 are simultaneously formed between the active layer stripes of the respective channels by selective growth, these portions are later removed by etching. After that, the mask for selective growth is removed, and the active layer stripe is embedded while forming the current block layer 7 as shown in FIG. Subsequent electrode forming steps and the like are similar to those of a normal semiconductor laser process.

As described above, in this embodiment, since the pitch of the diffraction grating is modulated and the peak wavelength of the gain is changed by selective growth, the oscillation wavelength and the detuning amount can be controlled independently by the elements of each channel, and the oscillation can be controlled. The wavelength can be greatly changed.

Next, a second embodiment of the present invention will be described. FIG. 2 is a view showing a method of manufacturing a distributed feedback laser array (four channels in this case) according to a second embodiment of the present invention. First, as shown in FIG.
A selective growth mask (usually using a SiO2 mask) 4 for forming active layer stripes is formed on the nP substrate 1. In this case, the mask width is 10 μm to 40 μm between adjacent active layer stripes every 10 μm. A mask is formed so that it becomes wider (the width of this mask may differ depending on the growth apparatus and growth conditions). Next, the lower SCH is selectively grown by using such a mask.
A layer, an active layer (also MQW) and an optical guide layer are sequentially grown to form an active layer stripe 5 as shown in FIG. Subsequently, on the active layer stripe 5 of each element, the pitch between adjacent ones is from 0.2 nm to 203.2 nm.
The diffraction grating 2 changing at intervals of 4 nm is formed. Such a diffraction grating having a different bite between adjacent ones can be easily formed by using electron beam exposure. Next, the regions other than the active layer stripes that have been selectively grown at the same time are removed by etching, and the active layer stripes are buried while forming the current block layer 7 as shown in FIG. 2D. Finally, the entire surface of the wafer is formed with a p-type InP clad layer and a p-type InGaAsP.
Embed with cap layer. Subsequent electrode forming steps and the like are similar to those of a normal semiconductor laser process. In this embodiment, the same effects as those of the first embodiment were obtained.

In the above embodiment, the case where an n-type InP substrate is used has been described, but a p-type substrate may be used.
An aAs substrate can also be used. The present invention is also applicable to a distributed reflection type semiconductor laser array.

[0016]

As described above, in the method of the present invention, the detuning amount can be reduced in each element by combining the method of pitch modulation of the diffraction grating and the method of gain peak wavelength control by selective growth by electron beam exposure or the like. A semiconductor laser array which is equally and can greatly vary the oscillation wavelength can be realized.

[Brief description of drawings]

FIGS. 1 (a) to 1 (d) are views showing a manufacturing process of a distributed feedback laser array according to a first embodiment of the present invention.

FIGS. 2A to 2D are diagrams showing a manufacturing process of a distributed feedback laser array according to a second embodiment of the present invention.

FIGS. 3A to 3C are views for explaining the principle of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-InP substrate 2 diffraction grating 3 InGaAsP layer 4 mask for selective growth 5 active layer stripe 6 unnecessary portion 7 current blocking layer

Claims (2)

[Claims] In a distributed feedback type or distributed reflection type semiconductor laser formed in an array on a semiconductor substrate, a step of forming a diffraction grating so that a pitch of the diffraction grating is slightly different between at least adjacent elements; A step of growing a light guide layer made of a second semiconductor different from the substrate so as to embed a diffraction grating thereon, and a step of selectively growing the light guide layer by using a selective growth mask having a different mask width between adjacent elements. Forming a laser active layer by performing the following steps. 2. A distributed feedback type or distributed reflection type semiconductor laser formed in an array on a semiconductor substrate by selectively growing at least adjacent elements using selective growth masks having different mask widths. Forming an active layer, further growing a light guide layer made of a second semiconductor different from the substrate on the active layer, and further reducing the pitch of the diffraction grating between adjacent elements on the light guide layer. Forming a diffraction grating so as to be different from each other, and further growing a cladding layer made of the same kind of semiconductor as the substrate so as to embed the diffraction grating thereon. .