JPH0637386A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To discharge heat through an end part electrode when the temperature of an active layer near an end surface is elevated and avoid an end surface breakdown by a method wherein the end part electrode whose width is larger than the width of a stripe trench is provided above the stripe trench. CONSTITUTION:A current blocking layer 2 is formed on a semiconductor substrate 1 and a stripe trench 3 is formed in the surface of the current blocking layer 2. The width C of the stripe trench 3 near an end surface 4 is a little larger than the width C near a center part 5. A cladding layer 6 is made of GaAlAs whose aluminum mixing ratio is 0.4 and which is doped with Zn as P-type impurities and formed on the current blocking layer 2. An active layer 7 is formed on the cladding layer 6. Another cladding layer 8 is formed on the active layer 7. A cap layer 9 is formed on the cladding layer 8. An end part electrode 11 is formed above a center part electrode 12 and the stripe trench 3. With this constitution, heat can be discharged from the active layer easily and an end surface breakdown can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having high output and long life.

[0002]

2. Description of the Related Art In recent years, many improvements have been made to semiconductor lasers having a double heterojunction structure having a high output. FIG. 7 shows a semiconductor laser disclosed in, for example, Japanese Patent Laid-Open No. 2-224288. FIG. 7 is a perspective view of the semiconductor laser. In this figure, a current blocking layer 32 is formed on a semiconductor substrate 31, and a stripe groove 33 is formed on the surface thereof. The stripe groove 33 is formed shallower than the current blocking layer 32 near the end face 34 and deeper than the current blocking layer 32 near the center 35. The clad layer 36, the active layer 37, and the other clad layers 3 are sequentially formed on the current blocking layer 32.
8, the cap layer 39 and the surface electrode 40 are formed.

[0003]

In the above semiconductor laser, however, the surface electrode 40 is formed at a position slightly apart from the end surface 41 so that the end surface 41 can be easily divided by cleavage. In the case of a low output (10 to 50 mW) semiconductor laser, there is no problem in the above-mentioned configuration. However, at a high output of about 150 mW, there is a drawback that the life is shortened. The present inventor has investigated the cause of this and found that it is due to the temperature rise of the active layer 37 near the end face 34. This active layer 3
The temperature rise characteristic of No. 7 is shown by the broken line in FIG. These Figure 4
7 and the active layer 37 from the end face 41 to about 20 μm in FIG.
The temperature rise is relatively high. It has been found that the reason is that the surface electrode 40 is not provided above the stripe groove 33 in the vicinity 34 of the end face, so that heat dissipation in this portion is bad.

Further, conventionally, the longitudinal length of the stripe groove 33 is about 600 μm, but if a semiconductor laser of this length is made to emit light with a high output, the life is shortened. The present inventor has investigated the cause of this, and since the operating current density of the active layer (the value of the current flowing through the semiconductor laser divided by the area of the active layer) is relatively large, the current that does not contribute to light emission is converted into thermal energy. It was found that the ratio increased and the end face was destroyed. Due to the above two drawbacks, when this semiconductor laser is continuously operated at an output of 150 mW and an ambient temperature of 50 ° C.,
The output drops significantly after about 400 hours. Therefore, the present invention has been made in view of the above-mentioned drawbacks, and provides a semiconductor laser of high output and long life by suppressing the temperature rise of the active layer near the end face and optimizing the length of the stripe groove. Is.

[0005]

In order to solve the above-mentioned problems, the present invention forms a current blocking layer on a semiconductor substrate and forms a stripe layer so that a current does not flow near the end face but a current flows near the center. Form. A clad layer, an active layer and a surface electrode are formed on the current blocking layer. As the surface electrodes, a central electrode extending over the entire width of the active layer and an end electrode located above the stripe groove and having a width larger than the width of the stripe groove and smaller than the width of the central electrode are formed. More preferably, the present invention sets the longitudinal length of the stripe groove to 950 to 14.
The thickness is 00 μm.

[0006]

As described above, the present invention provides the end electrodes located above the stripe groove and larger than the width of the stripe groove. Therefore, the active layer whose temperature has risen near the end face easily radiates heat through this end electrode. More desirably, by setting the longitudinal length of the stripe groove to be 950 to 1400 μm, the operating current density of the active layer is reduced, and the ratio of thermal energy converted into other than emission energy is reduced, so that the life is extended.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. 1 is a perspective view of a semiconductor laser according to this embodiment, FIG. 2 is a sectional view taken along line AA of FIG. 1, and FIG. 3 is a sectional view taken along line BB of FIG. In these figures, the semiconductor substrate 1 is made of GaAs doped with Zn as a P-type impurity and has a layer thickness of 70 μm.
Is. The current blocking layer 2 is GaA doped with N-type impurities.
s and has a layer thickness of about 1 μm, and is formed on the semiconductor substrate 1.

The stripe groove 3 is formed on the surface of the current blocking layer 2 and is shallower than the current blocking layer 2 near the end face 4 and does not reach the bottom surface of the current blocking layer 2. The stripe groove 3 extends into the semiconductor substrate 1 deeper than the current blocking layer 2 near the center 5. The longitudinal length of the stripe groove 3 near the end face 4 is about 20 μm, and the entire longitudinal length of the stripe groove 3 is 9 μm.
The thickness is 50 to 1400 μm. Stripe groove 3
Has a width C of 3 to 7 μm, and the width C in the vicinity 4 of the end face is formed slightly wider than the width C in the vicinity 5 of the center.

The cladding layer 6 has Zn added as a P-type impurity, is made of GaAlAs having an aluminum mixed crystal ratio of 0.4, and has a layer thickness of 0.5 to 0.8 μm, and is formed on the stripe groove 3 and the current blocking layer 2. Has been formed.

The active layer 7 is made of GaA with an aluminum mixed crystal ratio of 0.05.
made of 1As and having a layer thickness of 0.1 μm and an emission wavelength of 830
and is formed on the clad layer 6. The other clad layer 8 is made of N-type GaAlAs with an aluminum mixed crystal ratio of 0.4, has a layer thickness of 4 μm, and is formed on the active layer 7. The cap layer 9 is made of N-type impurity-added GaAs and has a layer thickness of 7 μm, and is formed on the other clad layer 8.

The surface electrode 10 is made of gold or the like and the cap layer 9 is formed.
Formed on. The surface electrode 10 is a narrow end electrode 1
1 and a wide central electrode 12. The central electrode 12 is formed on the cap layer 9 so as to extend over the entire width of the active layer 7, that is, 10 to 20 μm is left from the end of the cap layer 9. The end electrodes 11 are stripe grooves 3
Is formed on the cap layer 9 directly above. The width D of the end electrode 11 is larger than the width C of the stripe groove 3 and smaller than the width of the central electrode 12. Desirably, the width D of the end electrode 11 is set to 8 to 100 μm. The length E of the end electrode 11 along the stripe direction of the stripe groove 3 is desired to be about 20 μm. The reason is that if the length E of the end electrode 11 is sufficiently longer than 20 μm, the length of the central electrode 12 becomes short and the attachment becomes unstable when die-bonding to a submount or the like. Usually, the position of the cleavage plane varies in the longitudinal direction when the end face is cleaved, but if the length E of the end electrode 11 is sufficiently shorter than 20 μm, the central electrode 12 may be cleaved.

The front end face 13 and the rear end face 14 are coated so that the reflectances are 5 to 30% and 50 to 95%, respectively. The surface electrode 10 is provided with a hole 15 at a predetermined position so that the automatic die bonder machine can recognize the front end face 13 and the rear end face 14 separately. A back surface electrode 16 made of gold or the like is formed on the back surface of the semiconductor substrate 1. The semiconductor laser 17 is composed of these layers.

A submount 18 is provided so as to be connected to the semiconductor laser 17. Submount 18 is Si layer 19
A gold layer 20, a platinum layer 21, a gold layer 22, and an indium layer 23 are sequentially formed on the back surface of the. Semiconductor laser 1
The surface mount 10 and the indium layer 23 are alloyed by placing the submount 18 on the substrate 7 and heating the placing surface intensively. On the contrary, the semiconductor laser 17 may be mounted on the submount 18.

In the semiconductor laser 17 of this embodiment, the stripe groove 3 is formed shallower than the current blocking layer 2 near the end face 4 and deeper than the current blocking layer 2 near the center 5. Alternatively, a stripe groove may be formed uniformly shallower than the current blocking layer near the end face and near the center, and the high resistance layer may be formed on the active layer near the end face. As described above, the stripe layer of the present invention is formed so that the current does not flow near the end face and the current flows near the center.

Next, a temperature rise characteristic diagram of the active layer in the semiconductor laser of this embodiment is shown by a solid line 24 in FIG. Solid line 2
The characteristic diagram of No. 4 is the measured value when the width D of the end electrode 11 is 8 μm. As a result of the experiment, the temperature rise characteristic of the active layer depends only on the width D of the end electrode 11 and the length E of the end electrode 11.
It was found that it did not depend on the length of the stripe groove 3. Further, as the width D of the end electrode 11 is made larger than 8 μm, the temperature rise of the active layer 7 in the vicinity 4 of the end face becomes lower and the life becomes longer. However, if the width D of the end electrode 11 is made too large to be the same as that of the center electrode 12, cleavage becomes difficult, and steps or scratches occur on the front end face 13 and the rear end face 14, which is not practical. According to experiments conducted by the present inventor, if the width D of the end electrode 11 is 100 μm at the maximum, the end face is normal, but 100 μm.
It was found that the scratches were generated on the end surface when it exceeded.

Next, the characteristics of the maximum optical output in the semiconductor laser of this embodiment will be described with reference to FIG. The horizontal axis represents the resonator length, that is, the length (μm) of the stripe groove 3. The vertical axis represents the maximum light output (mw). As a result of the experiment, it was found that this characteristic does not depend on the width D or the length E of the end electrode 11. From this figure, it was found that the maximum optical output was almost saturated when the cavity length was 950 μm or more.

Further, characteristics of operating current density in the semiconductor laser of this embodiment will be shown. The horizontal axis represents the cavity length (μm), and the vertical axis represents the operating current density (kA / cm ² ) (the value of the current flowing through the semiconductor laser divided by the area of the active layer in which the current flows). In this figure, the resonator length is 950 to 140
It can be seen that in the case of 0 μm, the operating current density is smaller than 6 kA / cm ² . And the resonator length is less than 950 μm or 1
If the thickness exceeds 400 μm, the operating current density increases, and the current that does not contribute to light emission is converted into heat energy. This thermal energy causes the temperature of the current blocking layer 2 below the stripe groove 3 near the end face 4 to rise, causing the end face to be destroyed and shortening the life. On the other hand, if the resonator length is 950 to 1400 μm, 2000 hours of continuous oscillation can be achieved at an output of 150 mw and an ambient temperature of 50 ° C.

[0018]

As described above, the present invention provides the end electrodes located above the stripe groove and larger than the width of the stripe groove. Therefore, the active layer whose temperature has risen in the vicinity of the end face easily radiates heat through this end electrode, so that the end face can be prevented from being destroyed. Since the width of the end electrode is set smaller than the width of the central electrode, the end face can be easily cleaved so that no step or scratch is generated on the end face.

More preferably, since the operating current density of the active layer is reduced by providing the longitudinal length of the stripe groove in the range of 950 to 1400 μm, the current not contributing to light emission is converted into thermal energy. The ratio becomes smaller. Therefore, the temperature rise of the current blocking layer under the stripe groove near the end face is reduced, and the end face can be prevented from being destroyed, so that the life is extended.

[Brief description of drawings]

FIG. 1 is a perspective view of a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

3 is a cross-sectional view taken along the line BB of FIG.

FIG. 4 is a characteristic diagram of temperature rise of an active layer.

FIG. 5 is a characteristic diagram of the maximum optical output in the semiconductor laser according to the example of the present invention.

FIG. 6 is a characteristic diagram of operating current density in the semiconductor laser according to the example of the present invention.

FIG. 7 is a perspective view of a conventional semiconductor laser.

[Description of Reference Signs] 1 semiconductor substrate 2 current blocking layer 3 stripe groove 4 near end face 5 near center 6 clad layer 7 active layer 10 surface electrode 11 end electrode 12 center electrode

Claims (2)

[Claims] 1. A semiconductor substrate, a current blocking layer formed on the semiconductor substrate, and a stripe groove formed in the current blocking layer so that a current flows near the center and no current flows near the end faces.
A clad layer formed on the current blocking layer, an active layer formed on the clad layer, and a surface electrode, the surface electrode extending across the entire width of the active layer and the stripe groove. 2. A semiconductor laser comprising an end electrode located above and having a width larger than the width of the stripe groove and smaller than the width of the central electrode. 2. The semiconductor laser according to claim 1, wherein the stripe groove has a longitudinal length of 950 to 1400 μm.