JP2653986B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Related to the original compound semiconductor laser.

[0002]

2. Description of the Related Art In a compound semiconductor laser, how efficiently heat generated in a light emitting portion thereof, that is, an active layer is radiated to the outside, which has a great influence on laser characteristics and life.

Various types of compound semiconductor lasers have been proposed. Basically, as shown in FIG. 3, an energy band gap is provided between the active layer 3 and the active layer 3 as shown in FIG. The structure is such that the cladding layers 2 and 4 are large, have a small refractive index, confine carriers and light, and are lattice-matched.

For example, in the case of an AlGaInP quaternary semiconductor laser, an AlGaInP
First cladding layer 2 of compound semiconductor layer of P quaternary mixed crystal
An active layer 3 composed of a GaInP layer; and a second cladding layer 4 composed of a semiconductor layer having the same composition as the first cladding layer 2.
And a cap layer 5 made of, for example, GaAs are successively formed thereon by MOCVD (Metalorgnic Chemical Vapor D).
(eposition) or MBE (Molecular Beam Epitaxy). 6 and 7
Denotes electrodes that are ohmic-coated on the other main surface of the GaAs substrate 1 and the cap layer 5, respectively. The electrode 7 itself has a function as a heat sink, or is soldered to a heat sink 9, that is, a radiator provided separately from the electrode 7 by a solder layer 8.

As described above, the cladding layers 2 and 4 are made of, for example, a quaternary mixed crystal of AlGaInP and are made of GaAs.
However, from the viewpoint of heat conduction and the like, the thermal resistance increases as the number of constituent elements of the mixed crystal increases, so that the quaternary mixed crystal AlG
The cladding layer made of aInP has low thermal conductivity.

When the heat conduction of the cladding layer adjacent to the active layer is low, the heat generated from the active layer during operation is not effectively dissipated. Is disturbed, and dislocations occur in the active layer and the crystals in the vicinity thereof, and changes due to crystal growth occur, resulting in stability of laser characteristics and shortening of life,
In particular, the above-described quaternary short-wavelength oscillation laser such as an AlGaInP laser inhibits continuous oscillation at room temperature.

In a compound semiconductor, when a binary compound is further added with a constituent element to form a ternary mixed crystal, a decrease in thermal conductivity, that is, an increase in thermal resistance is caused by, for example, P.D. Solid-State Electronics, 67 10161-168 (PD May
cock; Solid-State Electronics, Pergamon Press), and there are systems whose thermal conductivity is reduced by more than one digit depending on the constituent elements.

[0008] It is known that heat in a compound semiconductor is mainly transmitted by phonons, but it is a factor of reducing thermal conductivity. 1 of this phonon scattering
One cause is, for example, in the case of III-V compound semiconductors, there is an effect of so-called disordering in which two elements are randomly occupied in the group III site.

[0009] Among phonons, those relating to heat conduction are LA phonons mainly having a large group velocity and a long mean free path.

[0010]

SUMMARY OF THE INVENTION The present invention relates to the above-described semiconductor laser, particularly, for example, an AlGaI which performs short-wavelength oscillation.
The purpose of the present invention is to reduce LA phonon scattering in the cladding layer of a quaternary semiconductor laser such as nP and improve thermal conductivity, thereby improving laser characteristics, lifetime, and continuous oscillation at room temperature.

[0011]

The present invention relates to a so-called quaternary semiconductor laser such as an AlGaInP semiconductor laser, for example, as shown in FIG. 1, wherein at least the cladding layers 12 and 14 provided in contact with the active layer 13 are provided. One is composed of a quaternary clad layer having a superlattice structure formed by periodically laminating thin film semiconductors of ternary mixed crystals, for example, AlInP and GaInP.

The cladding layer having the super lattice structure has
The average composition thereof has a required band gap difference and a refractive index difference with respect to the active layer 13, and is approximately the same as the above-described quaternary mixed crystal composition capable of exhibiting the effect of confining carriers and light in the active layer 13. The composition is selected according to the composition.

[0013]

According to the present invention described above, both or one of the cladding layers 12 and 14 have a superlattice structure to reduce the dimension of the mixed crystal, so that the scattering due to disordering in the mixed crystal is reduced. This increases the thermal conductivity here.

However, at the heterojunction, which is the interface between different types of semiconductors, when the LA phonon propagating in one crystal propagates into the other crystal, the LA phonon dispersion relation of the two types of crystals is changed. If there is no overlap,
LA phonons are scattered and cannot propagate. This is because momentum and energy cannot be conserved. Therefore, since there are many heterojunctions in the periodically superposed superlattice of different thin crystals, consideration must be given to the propagation of LA phonons. For example, each ternary AlInP layer and GaI
Superlattice (AlInP) _n (GaInP) _m by periodic superposition of thin film semiconductor with n and m atomic layers with nP layer
In the system, since the dispersion relation of LA phonons in both semiconductor layers AlInP and GaInP almost overlaps,
There is no particular problem regarding the LA phonon scattering related to the above. As for other systems, L is different in different types of semiconductor layers constituting the superlattice structure.
The dispersion curves of the A phonons are, for example, curves 21 and 22 in FIG.
Even though they are different from each other, each dispersion curve is folded down to 1 / (n + m) by so-called zone folding which is a feature of the superlattice structure.
Zones of dispersion curves 21 and 22 are shown at the left end in FIG.
Since the folded state is overlapped as schematically shown by a chain line and a broken line, the LA phonon can propagate without being scattered. Therefore, in the semiconductor laser according to the present invention, the thermal conductivity is increased in the cladding layer adjacent to the active layer 13 and, for example, heat is radiated to the heat sink 9 by efficient heat transmission.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIG. In the present invention, the quaternary first and second cladding layers 12 and 14 or the first cladding layer 12 on the heat sink side are formed by repeating a lower-dimensional mixed crystal ternary mixed crystal thin film semiconductor layer. The semiconductor layer has a superlattice structure with a periodic lamination structure.

The case where the present invention is applied to an AlGaInP quaternary semiconductor laser will be described. In this case, an n-type first cladding layer 12, an active layer 13, and a p-type first cladding layer 12 are sequentially formed on a substrate 11 made of, for example, n-type GaAs through a buffer layer of GaAs, if necessary, though not shown. 2 and the p-type cap layer 15 are MOCV
Continuous epitaxy is performed by D method, MBE method or the like. 16
Reference numerals 17 and 17 denote electrodes which are ohmicly attached to the other main surface of the substrate 11 and the cap layer 15, respectively. The electrode 17 itself has a function as a heat sink, or is soldered to another heat sink 19 by a solder layer 18 as shown.

As in the case of the active layer 13 and the cap layer 15 and the conventional AlGaInP quaternary semiconductor laser, the active layer 13 is made of GaInP and the cap layer is made of Ga.
It is constituted by As.

In the structure of the present invention, the first and / or second cladding layers 12 and / or
14 for AlInP and GaInP, respectively.
A superlattice structure of (AlInP) _n (GaInP) _m is formed by periodic superposition of thin film semiconductors with the original n and m atomic layers. The composition of the cladding layer having the superlattice structure is such that the average composition of the whole is required to exhibit the effect of confining carriers and light with respect to the active layer 13 in the original mixed crystal, in this example, AlGaInP. The composition having the required refractive index difference and the required energy band gap difference with respect to a certain amount of the active layer 13 is selected to be substantially the same.

Then, as shown by the broken line, the cap layer 1
The central portion is left in a stripe shape from the fifth side, and ions such as protons are selectively implanted to the left and right over a depth reaching the second cladding layer 14 to form, for example, a high-resistivity current confinement region 20. Thereafter, the electrodes 16 and 17 are attached, and the electrode 17 side is soldered to the heat sink 19 by the solder layer 18.

Incidentally, in the above-described example, the AlGaInP 4
This is the case where the present invention is applied to the original semiconductor laser,
The present invention can also be applied to other quaternary semiconductor lasers such as a GaInAsP semiconductor laser. In this case, at least one of the cladding layers can be formed as a ternary mixed crystal superlattice structure.

[0021]

As described above, according to the present invention, in a so-called quaternary semiconductor laser, at least one of the cladding layers adjacent to the active layer has a lower dimensional ternary than the quaternary. Since the thermal conductivity of the compound thin film semiconductor is increased as a superlattice structure to reduce the scattering of LA phonons, the temperature rise of the active layer 13 and the vicinity thereof can be effectively avoided. The stability of the above-mentioned characteristics, which are particularly problematic in the primary laser, and the improvement of the life,
Further, for example, it is possible to configure a semiconductor laser capable of continuous oscillation at room temperature in an AlGaInP-based short wavelength region.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional view of an example of a semiconductor laser according to the present invention.

FIG. 2 is a dispersion curve diagram of LA phonons used for explaining the present invention.

FIG. 3 is a schematic enlarged cross-sectional view of a conventional semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12, 14 1st and 2nd cladding layer 13 Active layer 15 Cap layer 16, 17 Electrode 20 Current constriction area

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Yoshifumi Mori Inventor, 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Masao Ikeda 7-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-62-51282 (JP, A)

Claims (1)

(57) [Claims] At least one of the cladding layers provided in contact with the active layer is constituted by a quaternary cladding layer having a superlattice structure formed by periodically laminating thin film semiconductors made of a ternary mixed crystal, and The quaternary mixed crystal whose average composition has a required band gap difference and a refractive index difference with respect to the active layer and has a carrier and light confinement effect in the active layer. It is selected to have the same composition,
A semiconductor laser having a higher thermal conductivity than a cladding layer made of only the quaternary mixed crystal.