JP2913652B2 - Semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable and high-output semiconductor laser.

[Conventional technology]

Conventionally used semiconductor lasers are of a current injection type, and have a double hetero structure in which a semiconductor serving as an active layer is sandwiched by a semiconductor having a larger band gap energy as a cladding layer. Further, in a usual 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 band gap larger than that of the central active layer in order to prevent the end face serving as the light reflection or emission face from being deteriorated or damaged. One example is a wind stripe laser (IE
Figure 2 shows the structure of the EE Journal of Quantum Electronics, QE-15, 775 pages (1979). By sandwiching the Al _0.06 GA _0.94 As active layer 103 between the Al _0.3 Ga _0.7 As cladding layers 102 and 104, a double hetero structure is formed on the GaAs substrate 101. First, all are formed as n ⁺ -type, then p-type impurities such as zinc are selectively diffused in the center other than near the end face, and the area from the surface to the active layer is
p ⁺ type. Thus, the central part of the active layer 103 is p ⁺ ,
The vicinity of the end face is assumed to be n ⁺ type. In the case of the same material, the n ⁺ type has a larger effective energy gap than the p ⁺ type, and thus the energy gap can be increased only near the end face. As a result, light absorption at the end face 109 is reduced, and the end face 1
09 deterioration and damage can be prevented, and high reliability and high output can be realized. This concept 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 area of the active layer is doped with p ⁺ or n ⁺ . For this reason, the crystal quality is reduced, and the absorption coefficient due to free carriers is increased, so that the oscillation threshold of the semiconductor laser is increased and the efficiency is reduced. Furthermore, since a pn junction must be taken between the active layer and the n-cladding layer,
Its diffusion is difficult to control. Further, since the region where the laser gain is applied has a high impurity concentration, there is a problem in reliability. The conventional structure has several disadvantages as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable and high performance semiconductor laser that eliminates the above-mentioned disadvantages by utilizing the properties of crystal growth and the properties of materials.

[Means for solving the problem]

The semiconductor laser of the present invention has an active surface formed of a ternary or higher III-V compound mixed crystal having different bond lengths between group III atoms and group V atoms in a crystal on a plane equivalent to the (001) plane. And a window structure formed of a III-V compound mixed crystal having the same composition as that of the active layer on the (111) plane formed on the emission end face, and an energy gap of the III-V compound mixed crystal of the active layer. Is smaller than the energy gap of the III-V compound mixed crystal having the window structure. It is important that the {110} end faces at both ends of the active layer formed on the (001) plane are formed by layers buried with the same composition as the active layer by growth on the (111) plane. Examples of III-V compounds having different bond lengths include GaInP, AlGaInP, GaInPAs, GaAsSb,
And so on, and applied in any case.

[Action]

It has conventionally been considered that the energy gap of a III-V compound mixed crystal is uniquely determined by its composition. But,
For example, organometallic thermal decomposition vapor deposition (MOVPE) (001)
Like GaInP and AlGaInP grown on the surface, the energy gap can be different depending on the growth temperature, the ratio of group V material to group III material in the gas phase (V / III ratio), impurity doping, etc. even if the mixed crystal composition is constant. (For example, the first volume of the 34th Spring Meeting of the 1987 Lecture Meeting on Applied Physics, 1st volume, lecture numbers 18p-ZA-4 and 28p-ZA-5 (1987
Year)). In other words, when a certain combination of the growth temperature and the value of the V / III ratio is used, the energy gap of GaInP or AlGaInP becomes
Greater than what is usually known for mixed crystals
It is shown to be as small as 50-90 meV.

The above description is for the case of growing on the (001) plane (the same applies to a plane equivalent to the (001) plane). However, for the case of growing on the (111) plane, the temperature or V / It always takes a normal value regardless of the III ratio. This is because Ga-P and I in GaInP
Al-P and In-PGa-P and In- in n-P or AlGaInP
The different bond lengths, such as P, occur in connection with immiscible regions. Therefore, Al-As in AlGaAs
This is a phenomenon that was not remarkably observed in the case where the bond lengths are almost equal to each other such as Ga and As. GaInAs, AlGaInAs, or Ga
Similar phenomena occur in a material such as AsSb which is composed of those having different group III-V bond lengths in the crystal. The function of the present invention will be described by taking Ga _0.5 In _0.5 P grown by MOVPE as an example. In this case, assuming that the growth temperature is 650 ° C. and the V / III ratio is 400, the energy gap Eg
Is 1.85 eV. This is known as the value of the Ga _0.5 In _0.5 P mixed crystal. 50 meV smaller than 1.90 eV. This 1.8
When a Ga _0.5 In _0.5 P layer of 5 eV is grown on the (111) plane, the energy gap takes a value of 1.9 eV. G
Applies to semiconductor lasers with a _0.5 In _0.5 P active layer. The center of the cavity is Eg to 1.85 eV Ga _0.5 In _0.5 P Ga _0.5 In
Ga _0.5 In _0.5 P formed with _0.5 P and grown on the (111) end face
1.9e at the laser beam exit surface
About V. Since the region where Eg is increased does not contribute to the laser gain, it is desirable that the region be kept to a necessary minimum. Therefore, the growth layer on the (111) plane is limited to 60 μm or less from the end face for the purpose of suppressing the rise of the oscillation threshold. Since laser oscillation occurs at a value determined by 1.85 eV, light absorption does not occur in the vicinity of the end face having a large Eg, so that optical damage and end face deterioration can be prevented. Further, it is not necessary to make the region for giving the laser gain a high impurity concentration. For this reason, a highly reliable and high output semiconductor laser can be realized. Further, as will be apparent from the next embodiment, the present structure can be realized more easily than the conventional example.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings, so that the configuration of the present invention will be more specifically shown.

FIG. 1 is a side view of an embodiment of the present invention. 60
An AlGaInP-based visible light semiconductor laser oscillating in a band at 0 nm will be described as an example. The n-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P cladding layer 2 and the Ga _{0.5 are formed} on the (001) n-type GaAs substrate 1 by MOVPE.
An In _0.5 P active layer 3, a p-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P cladding layer 4, and a P ⁺ -type GaAs cap layer 5 are sequentially grown. Active layer 3
Is grown at a temperature of 650 ° C., a V / III ratio of 400, and without impurity doping. Resonator total length is 200 ~ 300μm
Grooves extending in the direction perpendicular to the stripe direction (propagation direction of laser light) at intervals of 200 to 300 μm are formed by dry etching or the like so that a (111) plane having a depth of about 200 μm is protruded from the surface. Thereafter, a Ga _0.5 In _0.5 P layer 6 is selectively grown only on the (111) plane of the groove. Thereafter, the p-type electrode 7 is made of GaAs.
On the s contact layer 5, the n-type electrode 8 is
Formed. The end face 9 is formed by cleaving the portion where the Ga _0.5 In _0.5 P layer 6 is formed. The semiconductor laser obtained in this manner has a threshold rise of 5% or less as compared with a semiconductor laser without a Ga _0.5 In _0.5 P layer grown on the (111) plane, and the end face deterioration is reduced, so that the reliability is improved. Dramatically improved. In addition, the maximum light output was improved several times to prevent optical destruction of the end face. In addition, when this structure is formed, high reliability is high because high-concentration impurities are not introduced into a region for giving a laser gain.

In the embodiment shown here, the same effect can be obtained even if the p-type and the n-type are reversed. It goes without saying that other material systems can be applied as long as the conditions are satisfied. In the embodiment, the structure in which the active layer is sandwiched between the clad layers has been described. Similar effects can be obtained. Instead of a Fabry-Perot resonator type laser (Example), a DFB or DBR type laser having a diffraction grating may be used. As the stripe structure, any stripe structure such as an embedded type or 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 face due to light absorption of the end face, and to realize a semiconductor laser with higher reliability and higher output than the conventional one at low cost.

[Brief description of the 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... Ga _0.5 In _0.5 P layer on (111) plane, 7.
Type electrode, 8 ... n-type electrode, 9 ... end face, 102, 104 ... n
−Al _0.3 Ga _0.7 As cladding layer, 103 ... n ⁺ Al _0.06 Ga _0.94 As
Active layer, 105: diffusion region.

Claims (1)

(57) [Claims] 1. A ternary or more ternary II or III bond having different bond lengths between group III atoms and group V atoms in a crystal on a plane equivalent to the (001) plane.
An active layer formed of an IV compound mixed crystal and a III-V layer having the same composition as the active layer are formed on the (111) plane formed on the emission end face.
A window structure formed of a compound mixed crystal, wherein the active layer II
The energy gap of the IV compound mixed crystal is
A semiconductor laser characterized by being smaller than an energy gap of a II-V compound mixed crystal.