JPS6237908B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a distributed Bragg reflection type semiconductor laser device and a method for manufacturing the same.

Since continuous oscillation of semiconductor laser devices at room temperature was reported, many devices with various special functions have been developed. Of these,
Distributed Bragg Reflection (DBR) laser devices that utilize periodic irregularities (diffraction gratings) formed on the layer surface are capable of laser oscillation with a single wavelength determined by the period of the diffraction gratings, and their practical use is progressing. It is being

FIG. 1 is a schematic cross-sectional view showing the general configuration of a conventional DBR laser device. An optical waveguide layer 2, an active layer 3, and a cladding layer 4 are formed on a semiconductor substrate 1 by epitaxial growth or the like. here,
A heterojunction that emits light by current injection is usually formed between the active layer 3 and the optical waveguide layer 2 or cladding layer 4. After the growth of each layer 2, 3, and 4, the excitation region P is etched by photolithography, chemical etching, etc.
is formed in a mesa shape, and the non-excited region Q is the optical waveguide layer 2.
Etch and remove to the vicinity. Thereafter, irregularities with a constant period are formed on the surface of the non-excited region Q by two-beam interferometry or the like. By depositing electrodes 5 and 6 on the lower surface of the semiconductor substrate 1 and the upper surface of the excitation region P, respectively, the element structure shown in FIG. 1 is completed. Although the active layer 3 and the optical waveguide layer 2 may have the same composition, in order to reduce absorption loss in the non-excited region, the composition of the optical waveguide layer 2 is generally adjusted to match the emission wavelength of the active layer 3. However, it is preferable to use a transparent material.

However, this type of device has the following problems. That is, since the connection between the light emitting layer (active layer 3) in the excitation region P and the optical waveguide layer 2 in the non-excitation region Q is discontinuous, unnecessary reflection occurs at this discontinuity. For this reason, it is not possible to completely unify the oscillation mode. In addition, the above 2
When periodic irregularities are formed by beam interferometry, there is a possibility that the mesa shape of the excitation region P becomes a shadow and the irregularities are not formed on the surface of the optical waveguide layer 2 in the vicinity of the mesa portion. Further, even if the unevenness is formed, there is a problem that the desired unevenness shape and period cannot be obtained due to unnecessary interference from the vicinity of the meza portion.

The present invention was made in consideration of the above circumstances, and
The purpose is to provide a semiconductor laser device that is capable of low threshold operation and has excellent wavelength selectivity. Another object of the present invention is to provide a method for manufacturing the above-described semiconductor laser device.

First, an overview of the present invention will be explained. A structural feature of the present invention is that the light-emitting layer consisting of a heterojunction in the excitation region is formed so as to be substantially continuous with the maximum refractive index layer in the non-excitation region. The manufacturing method is characterized in that at least one semiconductor crystal layer of the same conductivity type as the substrate is grown on a semiconductor substrate, and irregularities with a predetermined period are formed on the surface of the maximum refractive index layer of this semiconductor crystal layer or a layer adjacent thereto. After that, an insulating film having striped rectangular windows is formed on the semiconductor crystal layer on which the unevenness has been formed, and then, using this insulating film as a mask, the semiconductor crystal layer is selectively etched to a depth that reaches the semiconductor substrate. At least one semiconductor crystal layer including a light emitting layer is then grown on the exposed semiconductor substrate.

Therefore, according to the present invention, since the connection between the light-emitting layer and the optical waveguide layer is substantially continuous, it is possible to prevent unnecessary reflections from occurring at the connection portion, thereby reducing the oscillation mode. Complete unification can be achieved. That is, wavelength selectivity can be improved. Moreover, since the stripe structure of the excitation region becomes a buried structure and no optical waveguide layer exists in the excitation region, the driving current can be reduced. That is, low threshold operation is possible. Furthermore, when forming periodic irregularities using two-beam interferometry or the like, there is no problem such as shadowing of the mesa part of the excitation region as in conventional methods, so the irregularities can be formed with high precision up to the vicinity of the excitation region. It has the effect of

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

FIG. 2 is a schematic cross-sectional view showing a schematic configuration of an apparatus according to an embodiment of the present invention. In the figure, reference numeral 11 denotes an N-InP crystal substrate, and the center portion of the upper surface of this crystal substrate 11 is slightly etched in a stripe shape. Then, the upper surface of the N-InP crystal substrate 11 except for the stripe-etched portion is N-etched.
In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 12 and N-InP
Crystal layers 13 are grown and formed. N-
On the surface of the InP crystal layer 13, irregularities with a constant period are formed. The period of this unevenness determines the oscillation wavelength, and is set to approximately 1900 [Å].
An insulating film 14 made of SiO ₂ or the like is formed on the upper surface of the N-InP crystal layer 13. here,
The crystal layer 12 has a bandgap corresponding to 1.15 [μm] in terms of wavelength, and this crystal layer 12 serves as an optical waveguide layer with a maximum refractive index.

On the other hand, an N-InP crystal layer 15, an N-InP crystal layer 15, an N-InP crystal layer 15,
In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 16, P-InP crystal layer 17 and P-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 18, respectively. They are grown and formed in the above order. Then, an electrode 19 is deposited on the lower surface of the N-InP crystal substrate 11, and P-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y)
An electrode 20 is deposited on the upper surface of the crystal layer 18 and the insulating film 14 . Here, the crystal layer 16 (active layer) has a band gap of 1.3 [μm] in terms of wavelength, and the crystal layer 18 has a band gap of 1.1 [μm] in terms of wavelength, and the electrode 20 has a band gap of 1.1 [μm] in terms of wavelength.
This is to reduce the contact resistance with the

With such a configuration, the crystal layer 16 becomes a light emitting layer, the crystal layer 12 becomes an optical waveguide layer, and the normal
Similar to the DBR laser device, it is possible to perform laser oscillation with a single wavelength determined by the period (1900 Å) of the unevenness formed in the crystal layer 13. In this case, since the light-emitting layer and the optical waveguide layer are connected substantially continuously, unnecessary reflection does not occur at the connection, and the oscillation wavelength can be completely unified. Further, since the excitation region including the crystal layer 16 serving as the light emitting layer has a so-called buried structure and the crystal layers 12 and 13 are not present in the excitation region, effects such as low threshold operation are achieved.

Next, a method of manufacturing the device of this embodiment will be explained. FIGS. 3a to 3e are schematic diagrams showing the manufacturing process of the example device. First, as shown in Figure 3a, N-
N-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) on the InP crystal substrate 11
A crystal layer 12 and an N-InP crystal layer 13 are sequentially grown. Then, using a two-beam interference method, a chemical etching method, etc. on the surface of the N-InP crystal layer 13,
As shown in Figure 3b, the irregularities (diffraction grating) have a predetermined period.
form. Next, on the N-InP crystal layer 13
An insulating film 14 such as SiO ₂ is attached, and this insulating film 14 is
A long striped rectangular window 14a is formed in the center of the diffraction grating in a direction perpendicular to the fringes of the diffraction grating. Then, using this insulating film 14 as a mask, each of the crystal layers 13 and 12 is selectively etched to a depth up to the crystal substrate 11 by a chemical etching method.
Incidentally, FIG. 3 d shows the state of the cross section taken along arrow AA in FIG. 3 c after the above-mentioned etching. Next, on the exposed N-InP crystal substrate 11, as shown in FIG.
As shown in FIG.
In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 16, P-InP crystal layer 17 and P-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 18 above They grow and form in order. Then, by applying the electrodes 19 and 20, respectively,
The device structure shown in FIG. 2 is obtained.

Thus, according to the method of this embodiment, the N-InP
When forming irregularities with a predetermined period on the surface of the crystal layer 13 by two-beam interferometry or the like, the irregularities can be formed with high accuracy because the surface is flat and there is no mesa part of the excitation region as in the conventional method. I can do it.
Furthermore, after selectively etching the crystal layers 12 and 13, the crystal layers 15 to 18, which will become excitation regions, are embedded in the etched portions.
N-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 16 (active layer) and N-In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer 12
(optical waveguide layer) can be formed continuously. Here, the active layer 16 may be slightly curved in the vertical direction as shown in FIG. 4 or 5 during the second crystal growth, but the active layer 16 and the optical waveguide layer 12 are As long as they are almost continuous, there is no problem.

Note that the present invention is not limited to the above-described embodiments, and can also be applied to, for example, a GaAs-GaAlAs system. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the general configuration of a conventional DBR laser device, FIG. 2 is a schematic cross-sectional view showing the schematic configuration of an embodiment of the device of the present invention, and FIGS. The schematic drawings showing the manufacturing process, FIGS. 4 and 5, are schematic cross-sectional views for explaining the operation of the above embodiment, respectively. 11...N-InP crystal substrate, 12...N-
In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) Crystal layer (optical waveguide layer), 1
3... N-InP crystal layer, 14... Insulating layer, 15...
...N-InP crystal layer, 16...N-
In ₍₁ - _x) Ga _x As _y P ₍₁ - _y) crystal layer (active layer), 17...
...P-InP crystal layer, 18...P-
In ₍₁ ― _x) Ga _x As _y P ₍₁ ― _y) crystal layer, 19, 20...
electrode.

Claims (1)

[Claims] 1. A step of growing a semiconductor crystal layer having at least one layer of the same conductivity type as the substrate on a semiconductor substrate, and a layer having the maximum refractive index of the semiconductor crystal layer or a layer adjacent to the layer having the maximum refractive index. forming a diffraction grating with a predetermined period on the surface of the semiconductor crystal layer; forming an insulating film having striped rectangular windows on the layer on which the diffraction grating is formed; and using the insulating film as a mask, the semiconductor crystal layer is It is characterized by comprising the steps of selectively etching in a stripe shape to a depth that reaches the semiconductor substrate, and growing at least one semiconductor crystal layer of a different conductivity type having a light emitting layer on the exposed semiconductor substrate. A method for manufacturing a semiconductor laser device.