JP2902697B2 - Semiconductor laser - Google Patents

Description

The present invention relates to an AlGaInP-based semiconductor laser capable of high-power operation.

(B) Conventional technology Conventionally, AlGaInP-based semiconductor lasers are known as short-wavelength semiconductor lasers. For example, IEICE Technical Report, OQE87-4
6, 115 (1989). FIG. 5 shows the structure of such an AlGaInP-based semiconductor laser.

In the figure, (11) is a substrate made of n-type GaAs, (12)
Is a buffer layer made of GaAs, (13) is an n-type clad layer made of n-type InAlP, (14) is an active layer made of undoped InGaP, and each of these layers is a well-known organic layer on one main surface of the substrate (1). It is formed epitaxially by metal chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

(15) is a p-type cladding layer made of p-type InAlP formed on the active layer (14), which has a stripe-shaped ridge (15a) extending in a direction perpendicular to the plane of the paper, and (16) is a p-type cladding layer. (15) p-type GaAs formed on top of ridge (15a)
(17) is a block layer of n-type GaAs formed on the p-type cladding layer (15) excluding the top of the ridge (15a), and (18) is a cap layer (16) and a block layer ( 17) A contact layer made of p-type GaAs formed thereon. (19) and (20) are n-type electrodes provided on the other main surface of the substrate (11) and on the cap layer (18), respectively.
And a p-type electrode.

The output power of such an AlGaInP-based semiconductor laser is increased by reducing the thickness of the active layer (14).
For example, when the layer thickness of the active layer (14) is 0.04 μm,
Continuous operation is possible up to an optical output of 20 mW.

However, in such an AlGaInP-based semiconductor laser, if the thickness of the active layer is made thinner than 0.04 μm in order to achieve higher output, the oscillation threshold current of the semiconductor laser sharply increases, and the device characteristics deteriorate. I do.

Therefore, as a structure for increasing the output of the semiconductor laser by a method other than reducing the thickness of the active layer, a so-called window structure that increases the band gap at the end of the laser cavity and reduces light absorption at the end face is proposed. Have been. For example, JP
In Japanese Patent No. 14986, the band gap at the end face is increased by providing a Zn diffusion region at the end of the laser resonator.

(C) Problems to be Solved by the Invention However, in the prior art, when a Zn diffusion region is formed, a crystal defect is apt to occur in this region, and this defect absorbs light and causes heat generation. Therefore, there was a problem of lack of reliability.

Accordingly, the present invention provides an AlGaInP-based semiconductor laser capable of high-output operation and having high reliability.

(D) Means for Solving the Problems The present invention provides a semiconductor laser in which an AlGaInP-based semiconductor layer forming a laser resonator is laminated on one main surface of a GaAs substrate, wherein one main surface of the substrate is {100} plane in the inner region of the laser resonator, and {1} at the end of the laser resonator.
It is characterized by being a plane inclined in the <011> direction from the 00 ° plane.

(E) Action According to the present invention, (100) of the laser cavity end of the substrate
The band gap of the semiconductor stacked on the plane inclined in the <011> direction from the plane becomes larger than the band gap of the semiconductor layer stacked on the (100) plane other than the end.

(F) Embodiment FIG. 1 shows an embodiment of the present invention. FIG. 1 (a) is a cross-sectional view of a plane perpendicular to the laser resonator, and FIG. 1 (b) is a cross-section in the laser resonator direction. It is XX sectional drawing of the same figure (a).

In the figure, (1) shows a resonator length of 350 μm and a chip width of 300 μm.
As shown in FIG. 3B, one main surface of the substrate is a (100) plane in the internal region (A region in the figure) of the m-type n-type GaAs. Area (area B in the figure)
Are inclined surfaces descending 5 ° from the (100) plane in the <011> direction. Such a region is formed by dry etching such as RIE and RIBE. In this embodiment, the length of each B region is set to 20 μm.

(2) has a layer thickness of 0.3 on one main surface of the substrate (1).
a buffer layer made of n-type Ga _0.5 n _0.5 P having a thickness of 1 μm; and (3) an n-type (Al) layer having a thickness of 1 μm laminated on the buffer layer (2).
_0.5 Ga _0.5 ) n-type cladding layer composed of _0.5 In _0.5 P, (4)
Is an active layer made of undoped Ga _0.5 In _0.5 P with a thickness of 0.08 μm laminated on the n-type cladding layer (3), and these layers are sequentially formed by using a well-known MOCVD method.

(5) is a p-type (Al _0.5 Ga) layer laminated on the active layer (4).
_0.5 ) _0.5 In _0.5 P p-type cladding layer having a ridge (5a) extending in the resonator direction. In the p-type cladding layer (5), the thickness of the thickest portion provided with the ridge (5a) is 1.0 μm, the thickness of the thinnest portion not provided with the ridge (5a) is 0.2 μm, and the thickness of the ridge (5a) is small. ) Top width is 5 μm.

(6) is a cap layer made of p-type Ga _0.5 In _0.5 P having a thickness of 0.1 μm laminated on the top of the ridge (5a) of the p-type cladding layer (5), and (7) is a cap layer other than the top of the ridge (5a). A block layer of n-type GaAs laminated on the p-type cladding layer (5), and (8) is a contact layer of p-type GaAs laminated on the cap layer (6) and the block layer (7).

(9) is a p-type electrode in which a Gr film and an Au film are applied in this order on the contact layer (8), and (10) is a Gr film, Sn film, and Au film on the other main surface of the substrate (1). Are n-type electrodes deposited in this order.

Thus, the present embodiment differs from the conventional apparatus in that one main surface of the substrate (1) is a (100) plane in the laser resonator inner area (A area) and the laser resonator end area (B area).
In this case, each of the AlGaInP-based semiconductor layers is stacked on the inclined surface which is lowered by 5 ° from the (100) plane in the <011> direction.

Therefore, the inclination angle of the main surface of the GaAs substrate (the inclination angle from the (100) plane to the <011> direction) is changed variously, and G
An a _0.5 In _0.5 P layer was formed, and its band gap energy was measured. The result is shown in FIG. Ga _0.5 In _0.5 P
The layer was formed using MOCVD at a growth temperature of 680 ° C. and a V / III supply ratio of 550, and the band gap energy was measured at a temperature of 10K. Similarly, on a GaAs substrate (Al _0.5 G
a _0.5 ) A _0.5 In _0.5 P layer was formed, and its band gap energy was measured. The results are also shown in FIG.

As is clear from the figure, the Ga _0.5 In _0.5 P layer, (Al _0.5 G
a _{0.5) 0.5} In _0.5 bandgap energy according to both P layer inclination angle increases also increases, the inclination angle in the 5 ° 0
°, the band gap energy of both layers increases by about 60 meV.

Therefore, also in the device of the present embodiment, each of the AlGaInP-based semiconductor layers has a band gap energy about 60 meV larger in the B region than in the A region. Thereby, in the device of the present embodiment, the band gap is increased in the laser cavity end region, so that light absorption at the end surface is suppressed,
End face destruction is prevented.

FIG. 3 shows the current-light output characteristics of the device of this embodiment. As can be seen from the drawing, in the device of the present embodiment, characteristics with good linearity without kink are obtained up to an optical output of 30 mW. From this, it can be seen that in the device of this example, the active layer (4) is bent at the interface between the region A and the region B, but does not affect the element characteristics. Next, a life test of the device of the present embodiment was performed by a constant output operation at an output of 20 mW and a temperature of 40 ° C. The result is shown by a solid line in FIG. For comparison, a semiconductor device similar to that of this example was stacked on a flat substrate, and a Zn diffusion region was provided at the end of the laser cavity, thereby producing a comparative device having a large band gap at the end face. , And its life test. The result is shown by a broken line in FIG.

As is clear from the figure, it can be seen that the device of this example has a significantly longer life than the comparative device. This is because, in the end region of the comparison device formed by Zn diffusion, there are many crystal defects due to excessive addition of impurities. The end region of the device of this embodiment is
Since it is formed only by lamination of semiconductor layers by MOCVD method,
This is considered to be because crystal defects are small in this region.

As described above, in the present embodiment, the inclination angle of the substrate in the region B is set to 5 °, but if it is 4 ° or more, it is enough to suppress light absorption at the end face, and if it is 7 ° or less, the inclined surface is inclined. It can be easily formed.

Also, each inclined surface of the substrate in the B region is <011>
One surface may be a surface rising in the <011> direction, and the other may be a surface rising in the <011> direction.

Further, in the device of this embodiment, when the cap layer (6) in the region B is removed, a GaAs / AlGaInP heterobarrier is formed in the region B, and it becomes difficult for current to flow. That is, since the current non-injection region is formed at the end, the optical end face destruction is further suppressed, and the output can be further increased.

(G) Effects of the Invention According to the present invention, one principal surface of the substrate is a (100) surface in the laser cavity inner region, and is inclined in the <011> direction from the (100) surface in the laser cavity end region. By stacking an AlGaInP-based semiconductor layer on top of this, the bandgap of the semiconductor layer in the end region becomes larger than the bandgap of the semiconductor layer in the internal region, reducing light absorption at the end surface. And high output can be achieved. Further, since the semiconductor layer in the end region in the device of the present invention can be formed only by the same process as the semiconductor layer in the internal region, the number of crystal defects is reduced, the life is extended, and the reliability is improved.

[Brief description of the drawings]

1 (a) is a sectional view showing an embodiment of the apparatus of the present invention, FIG. 1 (b) is a sectional view taken along line XX of FIG. 1 (a), and FIG. 2 is GaInP, AlGaInP with respect to the substrate inclined surface angle. FIG. 3 is a current-light output characteristic diagram of the device of the present embodiment, FIG. 4 is a life test characteristic diagram, and FIG. 5 is a cross-sectional view showing a conventional device.

Claims (1)

(57) [Claims] 1. A semiconductor laser in which an AlGaInP-based semiconductor layer forming a laser resonator is laminated on one main surface of a GaAs substrate, wherein one main surface of the substrate is $ 100 in an internal region of the laser resonator. ｛1 at the end of the laser cavity.
A semiconductor laser characterized by being a surface inclined in the <011> direction from the 00 ° plane.