JPS59172286A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To extract single wavelength laser beams with excellent directivity in the vertical direction to a P-N junction surface while inhibiting an unnecessary mode resulting from reflection by burying a light-emitting region and simplifying a lateral mode and reducing driving currents while confining beams changed into a uniaxial mode in a ring shape by using a diffraction grating. CONSTITUTION:A striped region 14 consisting of an InGaAsP active layer 2, a P-InGaAsP guide layer 3, a diffraction grating 4, a P-InP clad layer 5 and a P- InGaAsP contact layer 6 is formed on an N-InP substrate 1 to a ring shape with mutually parallel two straight line sections. The striped region 14 is buried by a P-InP optical confinement layer 7 and an N-InP current stopping layer 8. A projecting section 13, which is shaped along the direction of the striped region 14 and a section thereof takes an arcuate form, is formed to a section corresponding to one of both straight line sections of the surface on the electrode 9 side of the substrate 1. The semiconductor laser device avoids a utilization for an optical resonator of a section where a semiconductor crystal is directly in contact with the outside air such as a cleavage plane, utilizes periodic index distribution shaped in a liquid crystal for the feedback of beams, and reduces reflection resulting from a large refractive index difference.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single wavelength oscillation semiconductor laser device with good directivity.

Semiconductor laser diodes are small, vertical, or [&L
It has the characteristic of being capable of direct modulation, and various applications have been considered, and some have been put into practical use. However, the laser beam divergence angle is generally ≠00 to 600 (this is partly due to the diffraction effect caused by the small size of the light emitting part). For example, when used as a light source for original fiber transmission, In order to increase the coupling efficiency to the optical fiber, it was necessary to combine lens systems to form a -antiparallel beam. Setting this lens system requires a high degree of precision, and there are also problems with the long-term reliability of the lens system settings.

In addition, the fusing layer work was complicated because the element had to be placed close to the edge leakage of the heat sink. A surface-emitting laser is an attempt to solve this laser beam divergence angle by using a half-four diode and devising the -f diode itself without using a lens system.
Applied P] z3'aiast, 237
Zagu (7979)). However, because this laser has a short length that contributes to laser oscillation (hereinafter referred to as the laser length), the laser gain is small, and therefore the threshold current required for laser oscillation is high, making continuous operation at room temperature impossible. Not practical. In addition, in order to overcome this problem, there is an attempt to reduce the reflection loss by providing a distributed Bragg reflection layer and reduce the threshold current value (εI Applied Physics Society Him Conference gt'J Performance Collection P. /30.29a-b-7,298
-B-J), this requires the growth of 60 or more layers with two different refractive indexes and a thickness corresponding to l of the wavelength in the medium, which is difficult to manufacture. It hasn't happened yet.

Furthermore, a type of semiconductor laser that uses a diffraction grating to emit light from the top surface of the device in a direction perpendicular to the photoacoustic active layer has been proposed; -17+1fi82), in this 6q crisis, the transverse mode is not unified, so even if you try to obtain a single axis mode using a diffraction grating, you will not be able to obtain a single wavelength oscillation, and yt, The light intensity distribution at the extraction window does not have a single peak, and the coupling efficiency to the fiber cannot be improved. Furthermore, the #U crown also tastes good and is not practical.

On the other hand, a distributed feedback type using a diffraction grating (Distribu
tedfi'eedbaolc (hereinafter abbreviated as DIFB)
Lasers are being researched and developed for single-wavelength oscillation, but they require a pair of laser resonators (usually using a sheared crystal).
Once formed, laser oscillation is induced in the
7 Since single-wavelength light emission called the abli-velo mode becomes ineffective, one side of the open plane is usually chemically etched to create an inclined plane that is oblique to the active layer, and then It is safe to take measures such as covering all areas that are opaque to the laser output light, reducing the return light due to reflection, and suppressing the 7-apple bellows mode, which will not only complicate the device fabrication process but also However, the current required for launch was large, reducing efficiency.

The first vJ is an example of a conventional DFB laser, where l is n-
4 is a diffraction grating, 8 is a p-InGaAsP guide layer, 2 is an HGaAaP active layer, 5 is a p-InP cladding layer, 6 is a p-GaInA contact layer, and p-InP optical confinement. Layer 8 is an n-■nPi flow blocking layer, and 9 and 10 are N and Pi poles, respectively. or,
11 is a labor release surface, and 12 is an inclined surface. In this laser, the period of the diffraction grating 4 is an integral multiple of the shortest period corresponding to the laser oscillation wavelength, so the output light can be extracted in a direction perpendicular to the p-n junction surface or obliquely. The far-field image of the removed element is as shown in Figure 2. That is,
In the direction of the diffraction grating 4, it has a spread angle θI of 100#A due to the diffraction effect caused by the buried structure, and in the direction perpendicular to this, it has a very narrow spread angle 6 of about 03°. Therefore, if the surface shape of the n-substrate l is processed into a convex shape that protrudes in an arc shape along the stripes, the directivity can be improved. Third
! eXJ is an example of its application, and 1B is a processing part, and the distance IfJli from the upper surface of the substrate l to the light emitting surface is 81
If the refractive index of the substrate 1 with respect to the laser output light is h, then if the radius of curvature r is increased so that 11 r −−+−,g, the emitted light becomes parallel (θ,
4=0). For example, 5=700μm
For K, r=77 μm is found. This can be easily produced by using ion etching, chemical etching, or the like. This manufacturing method will be described in detail in Examples.

The above is perpendicular to the p-n junction plane of the conventional laser, and the 7 Apry-Perot mode, which is caused by reflection, tends to be mixed. This is because the air and the cow body, which have greatly different refractive indexes, are adjacent to each other, and light is reflected at the interface.

In order to eliminate these drawbacks, the present invention embeds the light emitting region to unify the mouse mode and reduce the driving current.
Using diffraction grating sound, the single-axis mode light is confined in a ring shape, suppressing the uneasy mode caused by reflection, and p −
This device extracts a single wavelength laser beam with good directivity in the direction perpendicular to the n-junction surface, and will be described in detail below with reference to the drawings.

Figures 1 and 5 show the structure of an embodiment of a semiconductor laser device according to the present invention. In these figures, parts corresponding to those in Figures 1 to 3 are designated by the same reference numerals. is attached. As shown in these figures, in this example, a p-nGaAsP active layer 2, a p-nGaAsP active layer 2, a p-nGaAsP active layer 2, a p-nGaAsP active layer 2,
A stripe region 14 consisting of an AsP guide layer 8, a diffraction grating 4, a p-tech nP cladding layer 5, and a p-tech nGaAsP contact layer 6 has two parallel linear portions on the n-tech nP substrate l. It is formed into a ring shape. and,
The stripe region 111 is filled with a p-1nP original confinement layer 7 and an n-type nP current blocking layer 8.

In this case, the fjl diffraction gratings are formed only in the straight portions of the stripe region 14, and the direction of the gratings is such that it intersects the direction in which these straight portions extend. Both I11. on the surface of the base ffl on the electrode 9 side. In a portion corresponding to one of the line portions, a convex portion 18 extending in the direction along the stripe region 14 and having an arcuate cross section is formed.

Thus, the semiconductor laser device according to this embodiment utilizes the portion of the semiconductor crystal, such as the open plane, which directly contacts the outside air, as an optical resonator. By using the periodic refractive index distribution provided inside the crystal as the original feedback, reflections caused by large refractive index differences are reduced.

Normally, a laser with this structure does not have a light extraction port, so it is necessary to separately provide an optical waveguide and take out the optical sound to the outside through this. Since light can be extracted in the direction perpendicular to the direction, there is no need to provide an optical waveguide or the like. The radius of curvature of the curved portion in the ring-shaped stripe region 14 of this proposal poses almost no problem in a normal buried structure optical waveguide even if loss due to bending is taken into account. For example, inflection double sound 3 of engineering nP
．． 2, the InGaAsP active layer 4 (
Calculations confirm that the equivalent refractive index for the emission wavelength /, 55 μm is 3.2≦3, and that the loss due to bending is extremely small, on the order of 0-' when the radius of curvature is 50 μm (' Bends 1nD
ielaotrio Guides' Be1l S
system Teahnioal Journal Vol.
4 # * & 7 (September / Wa 69), P
(See P 2103-2/32). Moreover, the loss due to this bending becomes smaller as the radius of curvature becomes larger. On the other hand, the detailed part is the original feedback? This is necessary for efficient generation, but this design has the advantage that it can be shorter than a normal DIFB laser because there are two straight sections. In other words, since it is possible to cause light oscillation in the straight portions of the pair and to guide optical sound in the curved portions, the semiconductor chip can be used efficiently. As described above, by using this structure, it is possible to oscillate a single wavelength element determined by the period of the diffraction grating 4 with good directionality.

Next, with reference to all of Figures 6 to 1II, the above-mentioned actual
A method for manufacturing a semiconductor laser device according to an example will be described.

First, as shown in FIG. 6, a 1nGaAsP active layer 2 is formed on an n-type nP substrate l by a liquid phase growth method, and a p-InGa layer having a larger energy transfer and decap than this active layer 2 is formed on an n-type nP substrate l by a liquid phase growth method or the like.
The AsP guide layer 8 and the like are firstly grown.

Next, as shown in Fig. 71A, the guide layer 8
On the upper surface of both ends, form a pattern of 15.15 (registration) using normal 7 otolithography technique, and
Bake after IU. Next, the film is thick on the entire top surface! ;00AF
7 Otre resist after NojJ? After spin-footing, the diffraction grating 40 striped pattern is exposed and developed using a conventional three-beam interference method, etc., and then p-InGa
A diffraction grating 4 is formed by etching the AsPI layer 8,
Roughly all the resists? Remove by plasma ashing method etc. (see Figures 9 and 10). In this case, the period A of the diffraction grating 4 is
．． L8. The equivalent refractive index determined by fi, the original confinement layer 7, and the 'd''i flow blocking layer 8 is set to λA=, 2·m (m is an integer of 2 or more), where λ is the n1 oscillation wavelength.

Next, a p-type np cladding layer 5, a p-1n
GaAaP contact layer 6t-ll by liquid phase growth method etc.
IiJ growth. Then, on the entire top surface, S10
．． The film 16 is formed by sputtering or the like. Next, the first/
As shown in FIG.
7 It is formed into a ring shape using the otolithography method, and this ring-shaped S10! A ring-shaped stripe region 14t'' is formed by etching using the film lff mask and using all of the bromine methanol solution. Next, as shown in FIG.
/# As shown in the figure, the p-type nP layer 7 and the n-type nP layer 8 are sequentially grown in the portions except for the stripe region 14 by a liquid phase growth method, etc., and then removed by etching 1 fl of the 5102 layer described above. do.

Next, a process of processing and forming a convex portion 18 having an arcuate cross section on the other surface of the substrate 1 will be described.

First, as shown in FIGS. 15 and 16, the Fg of the substrate l is
Using a previously prepared photomask, a thick rectangular resist is applied to a desired location on the T plane. Next, when this resist 17 is exposed to a high-temperature atmosphere and melted, the resist 17 becomes approximately arc-shaped in cross section in the width direction due to its viscosity, as shown in FIG. Next, as shown in FIG. Perform etching using ions, etc. If you do this, the resist 1? of the substrate l? The portion corresponding to the fully coated portion becomes a convex portion 18 whose cross section cut in the width direction is arcuate.

As explained above, according to the present invention, it is possible to extract light of a single wavelength in a direction perpendicular to the semiconductor substrate with good directivity and a unified transverse mode. Therefore, according to the present invention, it is easy to cut out pellets because the folded curved surface is not a concern, the coupling efficiency to the optical 7 eyer is high, and the radiation direction of the optical output is perpendicular to the p-n junction. Like a laser that obtains optical output from the folded surface, the mount is depressurized and there are no restrictions on the installation position of the mount or beam.Also, due to the structure, the original can be taken out perpendicular to the substrate, so it can be used in the same manner. A large number of pellets can be mounted on a heat sink, allowing them to emit light in an array.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing a conventional distributed feedback semiconductor laser device cut at -g, Figures 2 and 3 are perspective views showing other examples of the conventional distributed feedback semiconductor laser device, and Figure 3 is a perspective view showing other examples of the conventional distributed feedback semiconductor laser device. and FIG. 5 shows the structure of an example of this invention.
The figure is a plan view, Figure 5 is a cross-sectional view along the V-V line of Figure ψ,
Figures 6 to 1II show the manufacturing process of the same embodiment, and Figures 6, 10, and 10 are side views, and Figures 7, 9, 1/1, and 13. is a plan view, and Fig. 12 is the 1st/
ldr plane view along the line X1l-■ in the figure, Figure 11I is the 1st
The sectional views taken along y-WN in Figure 3 and Figures 15 to 1I show the process of machining a convex portion having an arcuate cross section.
Figure S is a plan view, Figure 16 is a sectional view taken along line M-XVI of Figure 1, and Figures 17 and 1 are the same sectional views. ■... Semiconductor substrate, 2... Active layer, 8
...Guide layer, 4...Grid, 5...
...Clad layer, 1B...Convex gL14...
...Stripe area. Traditional 6th figure JP-A-59-172286 (6)

Claims (1)

[Claims] A first conductivity type or second conductivity type active layer is formed on a first conductivity type semiconductor substrate, and a grating with a predetermined period is formed on the surface of the second conductivity type opposite to the active layer. a guide layer and a cladding layer of a second conductivity type, each of which has a stripe region including an antinodal layer stacked in sequence, and the stripe region is filled with a semiconductor having a refractive index smaller than that of the active layer. In a distributed feedback buried double heterostructure semiconductor laser device, a stripe region provided on the semiconductor substrate along the surface of the substrate is formed in a ring shape having a straight portion t in a part thereof, and a stripe region is formed on the semiconductor substrate along the substrate surface. The lattice is formed in a direction perpendicular to the direction in which the straight line portions extend,
and Item 11: A portion corresponding to the straight line portion on the surface of the semiconductor substrate opposite to the surface on which the stripe region is provided is formed into a convex portion extending in the direction in which the straight line portion extends and having an arcuate cross section; A semiconductor laser device characterized in that a portion of the convex portion is configured to serve as an outlet for a laser source.