JPS61156788A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To secure a confinement of carriers and to obtain the thermally stable characteristics of a semiconductor laser by a method wherein two layers of clad layers having the prescribed forbidden band width are provided in contact to the active layer and optical oozing layers are provided one by one in these clad layers. CONSTITUTION:A first clad layer 2 having the same conductive type as that of an N-type substrate 1, an active layer 3, a second P-type clad layer 4 and a P-type gap layer 5 are provided on the N-type substrate 1. A first optical oozing layer 21 and a second optical oozing layer 22, which ooze out from the layer 3 having the same conductive type as that of the layer 2 and the layer 4, are respectively provided in the layer 2 and the layer 4. In this case, the difference DELTAEg in energy band gap between the layer 3 and the layer 2 and between the layer 3 and the layer 4 are both selected in the condition of 0.35<=DELTAEg<=0.45eV. By this way, a thermal oozing of carriers can be suppressed. Accordingly, the dependency of the threshold current of the laser on heat can be lessened and the stabilization of the characteristics thereof can be contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to semiconductor lasers, particularly high-power semiconductor lasers.

[Conventional technology]

In increasing the output power of semiconductor lasers, optical loss at the light emitting end face, so-called COD (Ca tastro
ph 1c Optical Damage) becomes a problem.

In order to improve this COD, conventionally,
Various efforts are currently being made.

In other words, as shown in FIG. 1, a normal double heterojunction semiconductor laser is made of a substrate (1) of n-type GaAs and a substrate (1) of the same electric type, e.g.
a first cladding layer (2) made of s, an active layer 13) made of n-type, p-type, or intrinsic, e.g., GaAs; The active layer (3) and the first and second cladding layers (2) and (4) are epitaxially grown.
A heterojunction is formed between the two. FIG. 4 shows an example of an electrode stripe type structure, in which one electrode (7) is inserted through a striped electrode window (6a) formed in an insulating layer (6) formed on a cap layer (5).
is ohmically adhered to the cap layer (5). (
8) shows the other electrode provided on the substrate (1).

Figure 5 shows the distribution of the energy bandgap Eg near the active layer of this semiconductor laser.
), the energy band gap E is large compared to the energy band gap Eg1 of this active layer (3).
First and second cladding layers (2) and (4) having g2
) is arranged and a required gap difference ΔEg between the active layer (3) and the first and second claddings N (2) and (4)
At the same time, the difference in refractive index between the active layer (3) and the first and second cladding layers (2) and (4) confines the carriers in the active layer (3). Confinement is performed so that optical oscillation occurs.

In such a double junction semiconductor laser, CO
A typical example of improving O is the so-called SC, in which light confinement and carrier confinement are performed separately, and light confinement is performed widely to weaken the light intensity of the active layer.
H(5perate ConfinmentHete
structure). Figure 6 shows this SC
This shows the energy bandgap distribution of an H-type semiconductor laser, and in this case, the energy bandgap between the active layer (3) and the first and second cladding layers (2) and (4) is The difference ΔEg is smaller than the difference ΔEg
s, and is provided with first and second light seepage W4 (91 and 00) that has a confinement effect on carriers but allows light to seep out. .

Further, as another example, in the normal double junction type explained in FIG. 4, the thickness of the active layer (3) is 300 to 50.
There is one in which the pressure is sufficiently constant for approximately 0 people to cause light to substantially seep out from the active layer (3).

Furthermore, as the bandgap distribution is schematically shown in FIG. 7, thin first and second barriers ff (11) and (12
) was also proposed so that the seepage caused by the penetration of light actually occurred (Applied Physics Letters, ^pp1.phys).

Lett, 3B (11), I Ju
ne 1981).

[Problem that the invention seeks to solve]

However, the SCH type semiconductor laser shown in FIG. 6 described above has the problem that carriers are not sufficiently confined in the active layer and seep out due to heat, and that the threshold current tth has a large temperature dependence.

In addition, in the case where the active layer is made thin as described above or the barrier layer with a large energy gap is provided as explained in FIG. However, there is a technical problem in obtaining a layer with good crystallinity because it is necessary to increase the amount of Al added in the AlGaAs system, for example. and,
Since these thin layers are the active layer itself or a layer adjacent to the active layer, they have a large influence on the characteristics and pose problems in reliability and reproducibility.

As mentioned above, all of them have problems in increasing the power of COD, and it has not been possible to obtain a semiconductor laser with sufficiently high output power.'' [Means for solving the problem] In the present invention, a first cladding layer, an active layer, and a second cladding layer are sequentially provided, and the energy band gap difference ΔEg between the active layer and the first and second cladding layers is set to 0.35≦
ΔEg≦0.45 (eV), and a light seeping layer is provided on either one of the first and second cladding layers.Then, the energy band gap of this light seeping layer is The energy band gap is selected to be larger than the energy band gap of the active layer.

Here, the thickness da of the active layer is selected to be several hundred to 1,500 so that the same level of reliability and reproducibility as in a normal double heterojunction semiconductor laser can be obtained during epitaxial growth of the active layer. The distances ds□ and da2 between the active layer and the light seepage layer are similar to the reliability and reproducibility of the semiconductor layers that are interposed between the active layer and the light seep layer and constitute a part of each cladding layer. 50 mm, which is a thickness that allows light to seep out from the active layer.
Can be selected from 0 to 5000 people.

Also, the thickness of the light seepage layer may be several hundred, for example 500, as long as the epitaxial growth thereof is reliable and reproducible.

[Effect]

According to the above structure, by providing a light seepage layer with a smaller energy gap in the cladding layer, light seeps out from the active layer, thereby changing the light intensity distribution in the active layer to its peak. It can act to lower the value and widen its distribution. That is, since COD is determined by the value of the peak of light intensity, by lowering and widening the peak of light intensity, C00 is less likely to occur and higher output can be achieved. In particular, in the present invention, the energy band gap difference ΔEg in contact with active N(3) is 0.35 to 0.
45eV first and second cladding M(2) and (4)
It was confirmed that thermal carrier seepage can be effectively suppressed by confining the carriers, and the dependence of the threshold current Ith on heat can be reduced, and the characteristics We were able to stabilize the

〔Example〕

The present invention will be described in detail with reference to FIG. 1. In FIG. 1, parts corresponding to those in FIG. 4 are given the same reference numerals. In this example as well, for example, a first cladding layer (2) made of AIX Gat-x As of the same conductivity type is formed on an n-type GaAs substrate (11), and the n-type or p-plasticity is an intrinsic Any. an active layer (3) of Ga1-, As, and a p-type AlyGa1 of a conductivity type different from that of the first cladding layer (2).
A second cladding layer (4) made of −×^S and a cap layer (5) made of GaAs of the same conductivity type are formed, but in particular, the first and second cladding layers (2) are formed. and (4), ^12 Ga>- of the same conductivity type as these, respectively.
Light seepage from the first and second active M(3) consisting of 1As! (21) and (22) are provided. Specifically, a lower first cladding M (2A) which becomes a part of the first cladding layer (2) is epitaxially grown on the substrate (1), and then the first light seeps onto this. A layer (21) is grown epitaxially, on top of which a first cladding layer (
2) The first cladding on the upper layer that becomes part of! (2B) is epitaxially grown, and an active layer (3) is epitaxially grown thereon. Then, on top of this, there is a lower second craft layer (4) which becomes part of the second craft layer (4).
A) is epitaxially grown, a second light seepage layer (22) G is epitaxially grown on this, and an upper second cladding layer (4B) is epitaxially grown on this.

An insulating layer (6) is deposited on the cap layer (5), an electrode (7) is ohmically deposited through an electrode window (6a) formed in the insulating layer (6), and the other electrode (8) is deposited on the substrate (11). ) is ohmicly deposited.

Here each layer (2A) (21) <28) (3)
(4A) (22) (4B) (5) is continuously MOCVD (Mstaorganic Chemi
cal vapor deposition) by switching the feed gas.

The thickness da of the active layer (3) is, for example, 800, and the first
The second light seepage layers (21) and (22) each have a thickness da of 500 layers, and the upper first cladding layer (2B) and the lower second cladding layer (4A) The thickness dst and da2 of each are 500 people, and the first and second
The respective thicknesses of the light seepage layers (21) and (22) dcl
and dC2 are each, for example, 500 people. Furthermore, in the above composition of each layer, x, y, and 2 satisfy y>z>x. FIG. 2 shows the energy band gap Eg in each layer in this case, and the difference ΔEg in the energy band gap between the active layer (3) and the cladding layers (2) and (4) is 0.35≦ΔEg as described above. ≦0.45
(eV), active layer (3) and light seepage layer (2
Energy band gap between 1) and (22).

The difference ΔEgs is Δf! Let gs<ΔEg.

The curve shown by the solid line in FIG. 3 shows the light intensity distribution in this case. The broken line curve in the figure indicates the first and second crund layers (2
) and (4), light seeping layers (21) and (22
) shows the light intensity distribution when the structure shown in Figure 4 is not provided.As is clear from comparing both curves, the light intensity distribution is Compared to the steep intensity distribution, the light intensity distribution of the present invention is broader and its peak value is lower. In this way, the light intensity is weakened, COD is less likely to occur (and the integral amount, i.e.,
The total amount of light, and therefore the power, is sufficient.

In the above example, the present invention is applied to a ^1GaAs-based semiconductor laser;
It can also be applied to AsP optical semiconductor lasers and the like.

〔Effect of the invention〕

As described above, according to the present invention, the cladding layers (2) and (4) are provided in contact with the active layer (3) to confine light and carriers. ΔEg is selected to be 0.35 to 0.45 eV, and there is a light seepage layer (21) within these cladding layers.
By providing (22) and (22), it is possible to widen the light intensity distribution, improve COD, and therefore increase output, and furthermore, the cladding layer is provided in contact with the active layer to ensure carrier confinement. As a result, the temperature dependence of the threshold current 1th can be made small, and thermally stable characteristics can be obtained.

In addition, since the thickness of each semiconductor layer, especially the thickness of the active layer and the semiconductor layer in contact with it, does not need to be made very small, there is no need to reduce the thickness of the active layer and the semiconductor layer in contact with it. can also be avoided.

[Brief explanation of the drawing]

FIG. 1 is a linear cross-sectional view of an example of a semiconductor laser according to the present invention, FIGS. 2 and 3 are schematic diagrams of an energy band gap and a light intensity distribution curve, and FIGS.
The figure is a sectional view of a conventional semiconductor laser, and FIGS. 5 to 7 are schematic diagrams of energy band gaps for explaining each side of the conventional semiconductor laser. (1) is the substrate, (2) and (4) are the first and second cladding layers, (4) is the active layer, (21) and (22) are the first
and a second light seepage layer, (5) a cap layer, (6
) and (7) are electrodes.

Claims (1)

[Claims] A first cladding layer, an active layer, and a second cladding layer are sequentially provided, and the energy band gap difference ΔEg between the active layer and the first and second cladding layers is 0.3.
5≦ΔEg≦0.45 (eV), a light seeping layer is provided on at least one of the first and second cladding layers, and the energy band gap of the light seeping layer is is a semiconductor laser characterized in that the energy bandgap of the active layer is selected to be larger than that of the active layer.