JPS61279192A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To facilitate the growth of a crystal and to obtain a semiconductor laser, whose oscillating wavelength is high, by forming a diffraction grating for distribution feedback on the side surface of a mesa in an active layer. CONSTITUTION:A diffraction grating 10, which is effective in the direction in parallel with the direction of a current injection stripe electrode, is formed on one surface of an embedded surface 20, which is formed in a mesa shape with respect to the substrate surface. When a current is made to flow through a semiconductor laser, the current is confined in the active layer of an InGaAsP layer 4, whose band gap is the smallest, at the central part. Holes, which are injected from a P-InP layer 3, are combined with electrons, which are injected from an N-InP substrate 6 and an N-InGaAsP lightguide layer 5, in the active layer 4. Thus light is emitted. The light having a specified wavelength, which satisfies the Bragg reflecting conditions, is reflected and amplified in the diffraction grating 10. Oscillation occurs and the light is taken out of the end surface to the outside. Thus the semiconductor laser, whose oscillating wavelength is highly accurate, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used as a light source for, for example, optical fiber communication or optical measurement.

[Prior art C Figure 3 is a side view of Macoka et al. Electronics Letters Vol. 18, p. 27, 1982 (T.

MatSuoka at al,,EIgctra
18+27 (198'2) is a perspective IS view showing a conventional distributed feedback (DVB) type semiconductor laser shown in NJett, 18+27 (198'2), in which 1 is a p-electrode (anode), 2 is a p- rrxGaAsp camp layer, 3.
bap -r, n P craft layer, 4. is In Ga
A s P active layer, 5 n-rnGaAsp optical waveguide layer, 6 n-In serving as a craft layer.

A P substrate, 7 an n-electrode (cathode), 8 an n-UnP buried layer, and 10 a diffraction grating.

In Fapley-Bello (F P) type semiconductor lasers, which use a normal cleavage plane as a resonator reflector, even if a single longitudinal mode oscillates when DC current is injected, it becomes multi-mode during high-speed modulation. Changes in temperature also cause shifts in the oscillation wavelength. Therefore, if the reflecting mirror of the resonator is configured with a diffraction grating, it is possible to select a specific wavelength of light with more precision than the FP type, and it also does not become multi-mode even during high-speed modulation, and is also stable against temperature. Stable single-longitudinal mode oscillation is realized. In this way, high-speed, long-distance communication becomes possible by suppressing multimode oscillation and wavelength shift due to temperature changes. Therefore, what are called distributed feedback (DFB) type lasers and distributed reflection (DBR) type lasers in which a diffraction grating is incorporated into a semiconductor laser have been developed.

FIG. 3 shows an example of such a conventional distributed feedback type semiconductor laser, and its manufacturing method is as follows.

First, a diffraction grating 10 for distributed feedback is formed on the surface of the n-1nP substrate 6 by a three-beam interferometry method, etc., and then, by a liquid crystal epitaxial method, an n-InG
, aAsP layer 59 InGaAsP active layer 4 serving as a light emitting layer
．． The p-InP layer becomes the cladding layer, and the p-InP layer becomes the cap layer.
- Sequential crystal growth of InGaAs2 layer 2. moreover,
By etching both sides except for the part that will become the optical waveguide layer.
- Dig deep into the InP substrate 6. And again, n
-InP layer 8. The p-InP layer 9 is grown on the etched part so as to surround the active layer 4.Finally, the n-electrode 7 and the n-electrode 1 are attached and separated to an appropriate length. Make a semiconductor laser.

Next, the operation of this laser will be explained.

When a current is passed through this laser with the n-electrode being positive and the n-electrode being negative, the current is confined in the active layer of the InGaAs P layer 4 in the center, where the hand gap is the smallest, and the current flows through the p-InP layer. Holes injected from 3 and n-1n
P substrate6. Electrons injected from the n-1nGaAsP guide layer 5 combine within the active layer 4 to emit light. The emitted light travels back and forth within the n-1nGaAsP optical waveguide layer 5, and light of a specific wavelength is reflected and amplified by the diffraction grating 10 provided at the bottom of the optical waveguide layer 5, and eventually oscillates and is taken out from the end face. It will be done.

The injected current is n- except for one mesa in the center.
It becomes a pn type, and the current is blocked and does not flow, so it is confined in the center. In addition, light also has a small refractive index, p-1
nP cladding layer 9, l nGaAsP active layer 4, n-
Since it is confined within the 1nGaAsP optical waveguide layer 5, efficient laser oscillation can be achieved.

[Problem that the invention seeks to solve]

Conventional distributed feedback semiconductor lasers are constructed as described above, and since liquid phase crystal growth is performed after forming a diffraction grating on a substrate, the diffraction grating surface is melted back by the melt during growth, resulting in a decrease in diffraction efficiency. In addition, there have been problems such as difficulty in growing an optical waveguide layer and a thin active layer in a good manner.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a semiconductor laser that has a diffraction grating for a distributed feedback function and can also easily grow crystals.

[Means for solving problems]

In the semiconductor laser according to the present invention, an effective diffraction grating is formed on one side of the mesa for confining light and current in a direction parallel to the current injection stripe electrode, and
This mesa is buried with a cladding layer.

[Effect]

In this invention, the diffraction grating formed on the side surface of the mesa acts as a reflecting mirror for selecting a specific wavelength while the light generated in the active layer propagates in the optical waveguide layer.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a semiconductor laser according to an embodiment of the present invention, and FIG. 2 shows the manufacturing procedure of the device of this embodiment.
FIG. In the figure, the same symbols as in FIG. 3 indicate the same parts. In the figure, 1) is a resist for forming a diffraction grating 10, and 12 is an exposure laser beam irradiated onto the resist 1). In the device of this embodiment, the diffraction grating 10, which is effective in the direction parallel to the direction of the current injection stripe electrodes, is formed on one side of the buried surface 20 formed in a mesa shape with respect to the substrate surface. .

First, the steps for manufacturing the semiconductor device of the present invention will be explained with reference to FIG.

n-1nGaAsP optical waveguide layer 5 on n-1nP substrate 6
．． n-1nGaAsP active layer 4. p-1nP cladding layer 3. The p-InGaAsP cap layer 2 is successively crystal-grown by liquid phase epitaxial method or the like (Fig. 2(a)).
).

Next, mesa etching is performed, leaving the central part in a stripe shape (FIG. 2(b)). Then, resist 1) is applied to the mesa-shaped side surfaces formed on the 6th surface of the n-rnP substrate, one of the side surfaces is exposed by three-beam interference exposure method, and further etching is performed to provide distributed feedback to the mesa side surface. (FIG. 2(C)) After that, a p-1nP layer 9. is formed on both mesa parts. n-1nP layer 8
Embedded growth is performed using the method described above, the n-electrode 7° and the n-electrode 1 are attached, and the semiconductor laser chip is fabricated by cutting to an appropriate length (FIG. 2(d)).

Next, the operation of this laser will be explained.

When current is applied to this semiconductor laser with the n-electrode being positive and the n-electrode being negative, the current flows through the smallest InGa
Holes confined in the active layer of AsP layer 4 and injected from p-1nP layer 3 and n-rnP substrate 6, n-rnGaA
Electrons injected from the sP optical waveguide layer 5 combine within the active layer 4 to emit light. The emitted light propagates in the mesa stripe direction within the n-InGaAsP guide layer 5 and passes through the optical waveguide layer 5.
With the diffraction grating 10 provided on the side, Bragg
g) Light of a specific wavelength that does not meet the reflection conditions is reflected and amplified, and eventually oscillates and is taken out from the end face.

The injected current is n-p except for the mesa in the center.
- It becomes an n-type, and the current is blocked and does not flow, so it is confined in the center. In addition, light also has a small refractive index p-r
InGaAsP active layer 4+ by nPn tick 5 f9
Since it is confined in the n-1nGa7a and sP guide layer 5, efficient laser oscillation can be achieved.

In the above embodiment, the end face of the semiconductor laser is formed by cleaving, but one or both of the laser emitting end faces may be processed obliquely to the optical waveguide layer surface by etching or the like.

Furthermore, although there is a possibility that a distributed feedback semiconductor laser oscillates at three wavelengths, in order to prevent this, the phase of the grating may be shifted by 1/4 li1 period at the center of the diffraction grating.

Further, in the above embodiments, the case of a distributed feedback type semiconductor laser has been described, but a distributed reflection type semiconductor laser may also be used, and the same effects as in the above embodiments can be obtained.

Further, in the above embodiment, a semiconductor laser using an rnP-based material has been described, but it goes without saying that the present invention can also be applied to a semiconductor laser using other materials, such as a GaA3-based material.

〔Effect of the invention〕

As described above, according to the present invention, since the distributed feedback diffraction grating is formed on the mesa side surface of the active layer, crystal growth is easy and a semiconductor laser with high precision of the oscillation wavelength can be obtained. There is.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a semiconductor laser according to an embodiment of the present invention, FIG. 2 is a diagram showing a manufacturing procedure of the semiconductor laser of the above embodiment, and FIG. 3 is a perspective view showing a conventional semiconductor laser. l...n electrode (anode), 4...InGaAs
P active layer, 5-n-I nGaAsP optical waveguide layer, 6.
...n-1nP substrate, 7...n electrode (cathode), 1
0...Diffraction grating. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent early isiken - Fig. 1/7/-1" di2: I)-1nGaAsP@3:1)-1nP kupuku/□4 4°InGaAsP width + z, % 5:n-1nGaASP; Ijf#fjVii5, 'n
-InPl image figure 2 procedural amendment (voluntary) Showa Otsu θ year 'j'J], L day 2 Title of invention Semiconductor laser 3 Name of person making the amendment Name (601) Mitsubishi Electric Corporation 5 Amendment Column 6 of Detailed Description of the Invention in the Subject Specification, Contents of Amendment (1) “Confined” in Line 14 of Page 8 of the Specification
is corrected to "be trapped."that's all

Claims (3)

[Claims] (1) A semiconductor laser comprising a diffraction grating that is provided on at least one surface of a buried surface formed in a mesa shape with respect to a substrate surface and is effective in a direction parallel to a current injection stripe electrode. (2) The semiconductor laser according to claim 1, wherein one of the laser emission end faces is a cleavage plane perpendicular to the substrate surface, and the other is an oblique plane. (3) The semiconductor laser according to claim 1 or 2, characterized in that the phase of the grating is shifted by a quarter period at the center of the diffraction grating.