JP2593845B2 - Semiconductor light emitting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor light emitting device, particularly to a semiconductor laser.

[Summary of the Invention]

According to the present invention, the cladding layer for confining light and carriers in the active layer has a specified superlattice structure, and the effect of narrowing the current path can be exhibited by its conduction anisotropy.

[Conventional technology]

The basic structure of a compound semiconductor laser is the first on a substrate.
, An active layer, a second cladding layer, and a cap layer are sequentially epitaxially grown. The first and second cladding layers are formed of a semiconductor layer having a large energy band gap and a small refractive index as compared with the active layer to confine light and carriers in the active layer. Current narrowing means is provided for narrowing a current path between a pair of electrodes provided on the layer and on the back surface of the substrate to concentrate current injected into the active layer. As the current confining means, a stripe-shaped central portion for performing current concentration is left, and embedded on both sides to a depth from the cap layer side to the second cladding layer or in the second cladding layer. As described above, a method of providing a high resistance region or a current blocking region of a conductivity type different from that of the second cladding layer by, for example, selective ion implantation or a combination of mesa etching and epitaxy is adopted. However, the provision of such a current constriction means has a problem that the manufacturing process thereof is extremely complicated and it is difficult to obtain a specific target product uniformly and with good yield.

On the other hand, the present applicant has proposed that a semiconductor layer having a superlattice structure formed by alternately epitaxially growing a plurality of different kinds of semiconductor constituent material layers having a thickness of 8 atomic layers or less in a direction crossing the extremely thin semiconductor material layer. It has been found that high electron mobility can be exhibited with respect to. A semiconductor device based on this phenomenon has been proposed in Japanese Patent Application No. 60-52973.

[Problems to be solved by the invention]

The present invention provides a highly efficient semiconductor laser, that is, a semiconductor light emitting device, in which a current path can be defined without providing any special means such as the above-described current confinement region.

[Means for solving the problem]

In the present invention, as shown in FIG. 1, a buffer layer (not shown) is formed on one principal surface of one conductivity type, for example, an n-type compound semiconductor substrate (1), if necessary, and a substrate ( A first cladding layer (2) of the same conductivity type as in 1), an active layer (3), a second cladding layer (4) of another conductivity type, and a cap layer (5) of the same conductivity type in this order. MOCVD (Metalorga
nic Chemical Vapor Deposition or MBE (Molec
(Radial Beam Epitaxy).

Then, an insulating layer (6) is formed on the cap layer (5), and a striped window (6) is formed in the insulating layer (6).
Through a), one electrode (7) is used as a cap layer (5),
It is locally ohmically applied in a stripe shape corresponding to the inner shape of the window (6a). (8) shows the other electrode formed on the other surface of the substrate (1).

In the present invention, the first and second cladding layers (2) and (4) and the gap (5) are made of a plurality of different types of semiconductor constituent materials as shown in FIG. Ultrathin semiconductor material layers L ₁ , L ₂ , L ₃
.. are formed with a plurality of periods M alternately and repeatedly. That is, the heterojunction plane formed by the layers L ₁ , L ₂ , L _3, ... Is arranged substantially in the plane direction of the active layer (3).
Each layer L ₁ , L ₂ , L ₃ ... Is a single substance,
It can be constituted by a low-element-number mixed crystal of the original mixed crystal.

[Action]

According to the above configuration, the cladding layers (2) and (4)
Has an ultra-thin superlattice structure composed of each semiconductor material layer L ₁ , L ₂ , L ₃ ... Of 3 atoms or less, so that the window of the insulating layer (6) of both electrodes (7) and (8) Through 6a), a current path can be mainly formed only in the opposing portion.
This is due to conduction anisotropy in the semiconductor layer having an ultra-thin superlattice structure. That is, the mobility of carriers in the plane direction of the semiconductor layer of this ultrathin superlattice structure, that is, in the direction parallel to the heterojunction plane, depends on the thickness of each semiconductor material layer L ₁ , L ₂ , L _3. Is sufficiently small compared to the de Broglie wavelength of the semiconductor material layers L ₁ , L ₂ , L ₃ ..., The mobility in the mixed crystal due to the overall composition. Low mobility indicates low mobility. On the other hand, in the direction crossing the heterojunction plane, as described in the aforementioned Japanese Patent Application No. 60-52973, each semiconductor material layer L ₁ , L ₂ , L _3. Currently, LO
High mobility is exhibited by electrons not scattering with LO phonons due to phonon localization. Therefore, the current path can be formed in a limited manner only immediately below the portion where the electrode (7) is directly applied to the cap layer (5). That is,
The direction along the plane of the ultra-thin semiconductor constituent layers L ₁ , L ₂ , L ₃ ...
The electron mobility and mu _H of, when the electron mobility mu _V of this perpendicular to the direction (hereinafter referred to the longitudinal direction), μ _H «μ _V
Becomes On the other hand, the current I _{is, I = e ρ V = e} ρμE ...... (1) (ρ is the density of the carriers i.e. the electron, v is the carrier velocity, mu is mobility, E is the electric field) because it is given by, lateral Assuming that the current is I _H and the vertical current is I _V , I _H VI _V (2). As a result, the spread of the current in the horizontal direction is suppressed, and the current path becomes the cap of the electrode (7). The current path is limited immediately below the portion directly attached to the layer (5), that is, between the opposing portions of the electrodes (7) and (8), thereby obtaining a current constriction effect.

〔Example〕

In the configuration described with reference to FIG. 1, the first and second cladding layers (2) and (4) are made of (AlAs) _n (GaAs) _m by an AlAs layer doped with n-type and p-type impurities and a GaAs layer, respectively.
Each layer is composed of 1 to 3 atomic layers, that is, n and m are 1 to 3
A superlattice structure composed of an ultra-thin semiconductor constituent material layer as described above.

In the above-described example, both the first and second clad layers (2) and (4) disposed with the active layer (3) interposed therebetween have a superlattice structure, but the cap layer (5) side Second
In the case where only the cladding layer (4) has the above-mentioned superlattice structure, the current confinement effect can be exerted because the current spreading in the lateral direction is suppressed in this layer (4).

〔The invention's effect〕

As described above, in the present invention, at least one of the cladding layers is formed of a semiconductor layer having a superlattice structure formed by laminating an ultrathin semiconductor constituent material layer of 3 atoms or less, but now (AlAs) _n FIG. 3 shows the result of measuring the energy gap when n = m was changed for a (GaAs) _m- structured semiconductor layer. In the figure, black circles are plots of measured values. The dashed curve in the figure shows the energy gap obtained by calculation based on the Kronig-Penney theory. As is clear from the comparison with the dashed curve, Kronig- It has a small band gap that does not match the model of Penny. That is, 8 atomic layers or less, especially 1-3
It can be seen that at the atomic layer, electrons (charge particles) can be conducted in the stacking direction (vertical direction) without being localized.

As described above, in the present invention, at least one of the cladding layers has a superlattice structure of an ultra-thin semiconductor constituent material layer of 8 atomic layers or less, and the current path is restricted by the vertical mobility higher than the horizontal direction. This superlattice structure can be formed by a series of operations for the layers (2) to (5) by MOCVD and MBE, so that it is not necessary to provide a special current confining means as in the prior art. This eliminates the need for a complicated manufacturing process and improves the yield.

In addition, as described above, in the present invention, since the current path is limited only immediately below the electrode-attached portion only by the clad layer having the superlattice structure, the surface-emitting laser can be obtained by selecting the electrode-attached area.

Further, according to the present invention, by employing a superlattice structure, heat generated from the light emitting portion can be effectively dissipated, thereby stabilizing laser oscillation and extending the life. In other words, LA (Longi tudinal Acausti) which affects heat conduction in the superlattice structure
c) Good heat conduction is obtained by good propagation of phonons in the vertical direction. Especially, since the cladding layer in contact with the active layer has this super-lattice structure with good heat conductivity, the heat of the operating part can be efficiently dissipated. Can dissipate well.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view of an example of a semiconductor light emitting device according to the present invention, FIG. 2 is an explanatory view of a semiconductor layer having a superlattice structure, and FIG. It is a figure showing the measured value of the relation with the energy gap. (1) is a substrate, (2) and (4) are first and second cladding layers, (3) is an active layer, (5) is a cap layer, (7)
And (8) are electrodes.

Continuation of the front page (72) Inventor Yoshifumi Mori 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-60-13078 (JP, A) JP-A-61-131414 (JP, A) JP-A-61-78189 (JP, A) JP-A-60-130878 (JP, A) JP-A-61-184895 (JP, A) JP-A-61-210679 (JP, A) T . Yao: Jop. J. Appl, Phys. 22 (1983) PP. L680-682 Ezaki, Sakaki, "Superlattice heterostructure devices", Industrial Research Committee (1988) PP. 125-147

Claims (1)

(57) [Claims] 1. A semiconductor device comprising a semiconductor layer having a superlattice structure in which a plurality of different types of semiconductor constituent layers each having three atomic layers or less are alternately epitaxially grown. A semiconductor light emitting device characterized in that a current confinement effect is obtained in the light emitting operation region by cooperating with the conduction anisotropy of the lattice structure and an electrode provided locally corresponding to the light emitting operation region.