JP2527024B2 - Semiconductor laser - Google Patents

Description

The present invention relates to a highly reliable and high power semiconductor laser.

[Conventional technology]

Conventionally used semiconductor lasers are of the current injection type and have a double hetero structure in which a semiconductor to be an active layer is sandwiched with a semiconductor having a bandgap energy larger than that as a cladding layer. Further, in a general semiconductor laser, the composition of the active layer and the carrier concentration due to impurity doping are uniform over the entire cavity. However, it is known that it is effective to form the active layer in the vicinity of the end face with a material having a bandgap larger than that of the central active layer in order to prevent deterioration or damage of the end face serving as a light reflecting or emitting face. One example is the wind stripe laser (IE
Figure 2 shows the structure of the EE Journal of Quantum Electronics, QE-15, page 775 (1979). A double hetero structure is formed on the GaAs substrate 101 by sandwiching the Al _0.06 GA _0.94 As active layer 103 between the Al _0.3 Ga _0.7 As clad layers 102 and 104. First, all are formed as n ⁺ -type, and then p-type impurities such as zinc are selectively diffused in the central portion other than the vicinity of the end faces to form the surface to the active layer.
p ⁺ type. Thus, the central part of the active layer 103 is p ⁺ ,
The vicinity of the end face is n ⁺ type. In the case of the same material, since the n ⁺ type has a larger effective energy gap than the p ⁺ type, the energy gap can be increased only in the vicinity of the end face in this way. As a result, light absorption at the end face 109 is reduced, and the end face 1
The deterioration and damage of 09 can be prevented, and high reliability and high output can be realized. This idea can be applied not only to the AlGaAs system but also to other material systems.

[Problems to be Solved by the Invention]

In the above-mentioned prior art, the entire active layer is doped with p ⁺ or n ⁺ . For this reason, the crystal quality is deteriorated, the absorption coefficient is increased by free carriers, and the oscillation threshold of the semiconductor laser is increased and the efficiency is decreased. Furthermore, since the pn junction must be caught between the active layer and the n-clad layer,
It is difficult to control the diffusion. Further, there is a problem in reliability because the region where the laser gain is applied has a high impurity concentration. The conventional structure has some drawbacks as mentioned above.

Therefore, an object of the present invention is to provide a highly reliable and high-performance semiconductor laser that eliminates the above-mentioned drawbacks by utilizing the properties of crystal growth and the properties of materials.

[Means for solving the problem]

The gist of the present invention is that III-or more ternary elements having different bond lengths between the group III atom and the group V atom in the crystal are used.
A V compound mixed crystal is formed on the (001) plane to form a multilayer structure including an active layer having an energy gap smaller than the energy gap (normal value) of the bulk of the same mixed crystal composition,
A structure in which a layer of a III-V compound mixed crystal having a larger energy gap than the active layer and the same composition as that of the active layer is formed on the (110) end surface or the (10) end surface which is a light reflection surface or an emission surface. That is what I did. It is important that both end faces of the active layer formed on the (001) face are covered with crystals having the same composition as that of the active layer by growth on the face equivalent to the (110) face. There are many examples of III-V compounds having different bond lengths, such as GaInP, AlGaInP, GaInPAs, GaAsSb, etc., and they are applicable to any case.

[Action]

It has been conventionally considered that the energy gap of the III-V compound mixed crystal is uniquely determined by its composition. But,
If it falls down, it is (001) by metalorganic pyrolysis vapor phase growth method (MOVPE method)
Like GaInP and AlGaInP grown on the surface, the energy gap may be different even if the mixed crystal composition is constant, depending on the growth temperature, the ratio of the group V raw material to the group III raw material (V / III ratio) in the vapor phase, and the disordered doping. (For example, the 1987 Spring 34th Joint Lecture on Applied Physics, Proceedings of the 1st Volume, Lecture Nos. 28p-ZA-4 and 28p-ZA-5 (1987
Year)). That is, when a combination of a certain growth temperature and V / III ratio value is used, the energy gap of GaInP or AlGaInP becomes
Maximum than what is commonly known as the value for mixed crystals
It has been shown to be as small as 50 to 90 meV.

Also, the above is the case of growing on the (001) plane (the same applies to the plane equivalent to the (001) plane), but when growing on the (111) plane, the temperature at the time of growth by the MOVPE method or V / Regardless of the III ratio, the normal value is always 1.9 eV. This is Ga− in GaInP
P and In-P or Al-P and In-PGa-P in AlGaInP
It occurs in relation to the immiscible region due to the different bond lengths like In-P. Therefore, Al in AlGaAs
This is a phenomenon that was not noticeable in the case where bond lengths are almost equal, such as −As and Ga−As. Similar phenomena occur in GaInAs, AlGaInAs, GaAsSb, and the like, which are composed of different group III-V bond lengths in the crystal. The action used in the present invention will be described by taking Ga _0.5 In _0.5 P grown by the MOVPE method as an example. In this case, when the growth temperature is 650 ° C. and the V / III ratio is 400, the value of energy gap Eg is 1.85 eV. This is about 50 meV smaller than 1.90 eV, which is known as the value of Ga _0.5 In _0.5 P mixed crystal. When grown on the (110) plane at the same temperature and V / III ratio as the growth of this 1.85 eV Ga _0.5 In _0.5 P layer, the energy gap is 1.9.
Take the normal value of eV. This is applied to a semiconductor laser using Ga _0.5 In _0.5 P as an active layer. Eg to the center of the resonator
Eg at the laser light emitting surface is set to about 1.9 eV by forming Ga _0.5 In _0.5 P of 1.85 eV and covering the end face with Ga _0.5 In _0.5 P grown on the (110) plane. Since the region where Eg is increased does not contribute to the laser gain, it is desirable to keep the region to the minimum necessary. Therefore, in order to suppress the rise of the oscillation threshold low, the growth layer on the (110) plane is
Keep below μm. Since laser oscillation occurs at a value determined by 1.85 eV, light absorption does not occur near the end face with large Eg, and it is possible to prevent optical damage and end face deterioration. Further, it is not necessary to make the region for giving the laser gain a high impurity concentration.
Therefore, a highly reliable and high power semiconductor laser can be realized. Further, as is apparent from the next embodiment, this structure can be realized more easily than the conventional example.

〔Example〕

Next, the configuration of the present invention will be shown more specifically by explaining the embodiments of the present invention with reference to the drawings.

FIG. 1 is a side view of an embodiment of the present invention. 60
An AlGaInP-based visible light semiconductor laser that oscillates a band at 0 nm is shown as an example. The n-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P cladding layer 2 and Ga were formed on the (001) -faced n-type GaAs substrate 1 by MOVPE method.
_{A 0.5} In _0.5 P active layer 3, a p-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer 4, and a P ⁺ -type GaAs cap layer 5 are sequentially grown. The growth conditions of the active layer 3 are a temperature of 650 ° C., a V / III ratio of 400, and growth is performed without impurity doping. After that, the p-type electrode 6 is Ga
The n-type electrode 7 is formed on the substrate 1 side on the As contact layer 5. Cleavage is performed so that the total cavity length is 200 to 300 μm, and the Ga _0.5 In _0.5 P layer 8 is grown so as to cover at least the active layer 3 on the (110) plane or the (10) plane of the cleavage plane. This growth surface is referred to as a semiconductor laser light emitting end surface 9. The semiconductor laser thus obtained has Ga _0.5 grown on the (110) plane.
The threshold rise is 5 compared to a semiconductor laser without In _0.5 P layer
% Or less, and deterioration of the end face is reduced, so that the reliability is dramatically improved. In addition, the maximum optical output was improved several times because the optical destruction of the end face was prevented. Further, in the case of forming this structure, the growth on the (110) plane may utilize the cleavage plane of the crystal, and it is not necessary to form the (110) plane by etching or the like. Further, the high-concentration impurity is not introduced into the region which gives the laser gain, so that the reliability is high.

Similar effects can be obtained by reversing the p-type and the n-type in the embodiment shown here. Needless to say, other material systems can be applied as long as the conditions are satisfied. In addition, although the structure in which the active layer is sandwiched by the clad layers is described in the examples, other laminated structures, for example, a laminated structure in which an optical guide layer is provided adjacent to the active layer and the clad layer is arranged outside the same are also the same. The effect of is obtained. Further, a DFB or DBR type laser provided with a diffraction grating may be used instead of the Fabry-Perot resonator type laser (embodiment). As the stripe structure, any stripe structure such as a buried type and a planar type can be applied.

〔The invention's effect〕

As described above, by adopting the structure of the present invention, it is possible to prevent deterioration and damage to the end surface due to light absorption on the end surface, and it is possible to realize a semiconductor laser with higher reliability and higher output than ever before at a low cost.

[Brief description of drawings]

FIG. 1 is a schematic side view of an embodiment of the present invention, and FIG. 2 is a schematic side view of a conventional example. 1,101 ... n-GaAs substrate, 2 ... n- (Al _0.4 Ga _0.5 ) _0.5
In _0.5 P clad layer, 3 ... Ga _0.5 In _0.5 P active layer, 4 ...
… P- (Al _0.5 Ga _0.6 ) _0.5 In _0.5 P clad layer, 5 …… p ⁺
GaAs cap layer, 6 ... P-type electrode, 7 ... N-type electrode, 8
…… (110) Upper Ga _0.5 In _0.5 P, 9 …… End face, 102,104 ……
n-Al _0.3 Ga _0.7 As clad layer, 103 ... n ⁺ Al _0.06 Ga _0.94 A
s Active layer, 105 ... Diffusion region.

Claims (1)

(57) [Claims] 1. An energy gap of a ternary or more III-V compound mixed crystal having different bond lengths between the group III atom and the group V atom in the crystal and having an energy gap smaller than the bulk energy gap of the same mixed crystal composition. A multi-layered structure including an active layer having a (001) plane or a plane equivalent to the (001) plane, and a (110) end plane or a (110) plane that is a light emission plane, A semiconductor laser, wherein a III-V compound mixed crystal layer having a larger energy gap than that of the active layer and the same composition as that of the active layer is provided on the end face.