JPH067638B2 - Semiconductor laser device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used for recording / erasing an optical disk and for a medical or other high-power infrared laser light source.

2. Description of the Related Art In recent years, semiconductor laser devices have read signals on optical discs such as CDs, light sources for laser beam printers,
And, it has come into the spotlight as a central device of the optical industry for optical communication.

In most of these optical information devices, the demand for the laser light output was 10 to 20 mW or less. However, in recent years, demands for recording / erasing optical disks, speeding up printers, and high output (20 mW or more) laser devices for medical devices have been increasing.

There are two obstacles in promoting higher output of semiconductor lasers.
There is one. One is that when the output power is increased, the mode of the optical electric field propagating in the crystal easily moves from the fundamental mode to the higher order mode as the light density in the laser crystal increases. When oscillating in a higher order mode, the intensity distribution of the laser beam emitted from the crystal facet does not have a single peak, but has a plurality of peaks, which is a serious obstacle to practical use. This problem has been solved by reducing the thickness of the oscillation region (active layer) in the laser crystal. And BTRS (Buried Twin Ridge Subs)
In the trate) laser, a continuous oscillation output of 200 mW or more is obtained by thinning the active layer and improving the current injection efficiency. (Technical report of IEICE ED84-94
(1984)) The second point is that as the optical density at the laser crystal end face increases, deterioration near the end face progresses and the life of the laser shortens. It has been reported by Todoragi that the heat dissipation at the laser facet is poorer than that inside the crystal, and that the temperature locally rises to 200 ° C. or higher in the oscillation region near the facet. (Journal of Applied Physics 58, p.1124 (1985)) This local heat generation promotes dislocation generation and multiplication in the crystal,
The dislocation becomes a non-emissive center and absorbs the laser light to generate further heat, which repeats a vicious cycle (thermal runaway), which significantly shortens the life.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention reduces the light density of laser light at the crystal end face of a semiconductor laser, reduces the generation of heat at the end face, and damages the end face due to heat and reliability due to thermal runaway during laser operation It is intended to provide a semiconductor laser device having a long life and preventing deterioration of the semiconductor laser device.

Means for Solving the Problems In order to solve the above problems, the semiconductor laser device of the present invention has a stripe-shaped projection formed on the surface of a semiconductor substrate of one conductivity type, except for the vicinity of both end faces of the substrate, A layer of a conductivity type opposite to the one conductivity type is formed on the surface of the substrate, and from the surface of the layer of the opposite conductivity type, reaches the protrusion directly above the protrusion, and both end surfaces of the substrate without the protrusion. In the vicinity, a stripe-shaped window having a depth that does not reach the substrate is formed, and two ridges parallel to each other are formed on both sides of the groove so that the width becomes narrow near both end faces of the substrate. Each layer including an active layer is formed on the substrate having the ridge.

Action The semiconductor laser device of the present invention has the above-described structure so that the thickness of the active layer at the end faces of both resonators of the laser crystal is smaller than that inside the crystal, and no current flows through the end faces.
By thinning the active layer at the end face portion, the beam diameter of the laser light at the end face portion becomes large and the light density is reduced. Further, by not passing a current through the end face portion, heat generation inside the crystal near the end face is eliminated, and the temperature rise is prevented. Due to these two effects, it is possible to suppress the occurrence of deterioration at the laser end face, and to realize a laser device with high output and long life.

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

FIG. 1 shows a cross section of a semiconductor laser device according to an embodiment of the present invention. FIG. 1 (a) shows a cross section near the end face, and FIG. 1 (b) shows a cross section inside thereof. P-type GaA
The n-type GaAs block layer 2 on the s substrate 1 is for blocking the current, and in the cross-sectional view shown in FIG. 1 (a), this is continuous, so that no current flows near the end face. As can be seen in the cross section of FIG. 1 (b) inside the crystal, there is a mesa 9 on the GaAs substrate 1, and the groove 10 provided in the n-GaAs current block layer 2 reaches the mesa 9. Current is injected into the active layer 4 through 10. The ridge 11 of the n-GaAs block layer 2 has a G
This is for facilitating the control of the film thickness of the a _1-x Al _x As active layer 4. That is, the fact that the crystal growth rate becomes slower in liquid phase growth on the ridge 11 is used.

FIG. 2 shows a part of the manufacturing process of the semiconductor laser of the present invention. A mesa 9 is formed on the P-type GaAs substrate 1 by etching. The length of the mesa is 200 μm, the height is 3 μm, and the width is 10 μm. The resonator end face is formed by cleavage at the front and back of the mesa (Fig. 2 (a)). Next, the mesa is filled up by the liquid phase epitaxial growth method, and the first growth is performed so that the surface becomes flat (FIG. 2 (b)). The film thickness of the n-type GaAs block layer 2 on this mesa 9 is 1.0 μm.
m. The ridge 11 and the groove 10 are formed by etching. (Fig. 2 (c)). The depth of the groove 10 is 1.5 μm
Then, the groove 10 reaches the mesa 9 at the portion where the mesa 9 is present. Thus, the current can flow from the groove in the part where the mesa 9 is present, and the current can be stopped in the part where the mesa 9 is not present. At this time, the width of the ridge 11 is made narrower in the portion without the mesa 9. That is, it is set to 20 μm in the portion with the mesa 9 on one side of the groove and 5 μm in the portion without the mesa 9. Then, the second liquid phase epitaxial growth is performed on the substrate shown in FIG. 2 (c) to grow the multilayer structure shown in FIG. 1 (b).
At this time, since the growth rate on the ridge becomes slower as the width of the ridge becomes narrower, the active layer 4 becomes thinner at the end face portion where the width of the ridge is narrower than that inside the crystal. If the active layer 4 is thin, the light confinement becomes poor, and the beam diameter of the laser light becomes large near the end face. Therefore, the light density can be reduced. After the electrodes 7 and 8 are vapor-deposited, the resonator end face is formed by cleavage, and at this time, the cleavage position is such that the distance between the mesa 9 and the end face is 20 μm.

FIG. 3 shows current-to-optical output characteristics of a laser device in which the width of the ridge is narrowed by not injecting current into the end face portion and a device without these measures. A decrease in light density at the end face and a significant increase in saturation power are seen due to the suppression of heat generation. FIG. 4 shows a change with time of the operating current in the constant optical output drive. The rage element without the measures according to the present invention has a short life at high output, but the element according to the present invention has a sufficiently practical life.

As described above, according to the present invention, by providing the current non-injection region near the end face and thinning the active layer at the end face portion, the life of the semiconductor laser device can be remarkably extended, and its practical effect is There is a great one.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a perspective view showing a part of a manufacturing process of a semiconductor laser of the present invention, and FIG. 3 is a semiconductor laser. FIG. 4 is a characteristic diagram showing the relationship between the device current and optical output, and FIG. 4 is a characteristic diagram showing the change over time of the operating current of the semiconductor laser device when driven with a constant optical output. 1 ... P-type GaAs substrate, 2 ... n-type GaAs block layer, 3 ...
... P-type G _a1-7 AlyAs clad layer, 4 ... G _a1-x AlxAs active layer, 5 ... n-type G _a1-y AlyAs clad layer, 6 ... n-type GaAs
Layer, 7, 8 ... Electrode, 9 ... Mesa, 10 ... Groove, 11 ...
…ridge.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Ken Hamada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-158685 (JP, A) JP-A-60-789 (JP, A)

Claims (2)

[Claims] 1. A stripe-shaped protrusion is formed on the surface of a semiconductor substrate of one conductivity type except for the vicinity of both end surfaces of the substrate, and a layer of a conductivity type opposite to the one conductivity type is formed on the surface of the substrate. From the surface of the layer of the opposite conductivity type, a striped window having a depth that reaches the protrusion directly above the protrusion and does not reach the substrate in the vicinity of both end faces of the substrate without the protrusion is formed. Two ridges parallel to each other are formed on both sides of the groove so as to have a narrow width in the vicinity of both end faces of the substrate, and each layer including an active layer is formed on the substrate having the ridge. A semiconductor laser device characterized in that 2. The width of the ridge near both end faces is 5 to 5 on one side of the groove.
10 μm, the width of the ridge inside the resonator is 20 to 20 on either side of the groove.
2. The semiconductor laser device according to claim 1, wherein the length of the narrowed portion of the ridge is 10 to 50 .mu.m, and there is no protrusion near both end faces.