JPH07105557B2 - Semiconductor laser - Google Patents

Description

The present invention relates to a structure of a semiconductor laser capable of oscillating in a fundamental transverse mode and oscillating at a low threshold current density (hereinafter referred to as Ith).

[Prior Art] The structure of a conventional semiconductor laser is Al _x Ga _{1-x in the} film thickness direction.
The current confinement and optical confinement layers are formed by embedding an Al _x Ga _1-x As based semiconductor layer having a smaller refractive index than the active layer in the direction parallel to the junction surface using a double heterostructure of As / GaAs. there were. However, this conventional technique has a problem that since the embedded Al _x Ga _1-x As layer has a low specific resistance, current leakage occurs in a region other than a desired oscillation region, which is not effective in reducing Ith. Therefore, it was devised that a stripe-shaped rib was formed in the current confinement and optical confinement layer using a II-VI group semiconductor layer having a high specific resistance to a depth midway between the clad layers directly above the active layer, and Both ends are II-VI
It was a semiconductor laser embedded with a semiconductor layer made of a group compound semiconductor.

[Problems to be solved by the invention]

However, the above-mentioned conventional technique does not show the optimum value of the angle θ formed between the side surface of the rib and the joining plane, and if θ is too large, the width of the active region can be reduced. This makes it difficult to oscillate a higher-order mode light in the transverse oscillation mode, and there is a problem that a minute spot for writing and reading in the optical information recording device cannot be obtained. Further, if θ becomes too large, the width of the injection current becomes wide, the threshold current becomes high, and the astigmatic difference becomes large. If θ is too small, the clad layer must be thin to obtain the desired active layer width. Therefore, the amount of light leakage increases and the oscillation threshold value rises, resulting in oscillation output. It had a problem that it could not be expensive.

Therefore, the present invention solves such a problem, and its purpose is to provide an effective light confinement effect.
An object of the present invention is to provide a semiconductor laser which can control oscillation only in the fundamental transverse mode, has a low oscillation threshold, and can stably oscillate up to a high output.

[Means for solving problems]

The semiconductor laser of the present invention has a stripe-shaped rib formed up to an intermediate depth of the clad layer directly above the active layer of the double heterojunction type semiconductor laser composed of the active layer and the clad layer made of a III-V compound semiconductor. In a semiconductor laser in which both ends of the rib are filled with a semiconductor layer made of a II-VI group compound semiconductor, the angle θ formed between the side surface of the rib and the bonding plane is 50 ° to 120 °. It has a feature.

〔Example〕

FIG. 1 is a main sectional view of a semiconductor laser according to an embodiment of the present invention. 103 n-type Ga on a 102 n-type GaAs single crystal substrate
As buffer layer, 104 n-type AlGaAs cladding layer, 105 GaAs
Alternatively, it is composed of an AlGaAs active layer, a P-type AlGaAs clad layer formed in a reverse mesa-shaped rib type 106, and a P-type GaAs contact layer 108, and both ends of the rib are filled with 107 II-VI group compound semiconductor such as ZnSe. Has been. The ZnSe layer on the upper surface of the contact layer 108 is removed by an etching process, and a P-type ohmic electrode 109 is formed. An n-type ohmic electrode 101 is formed, and a current is passed between the electrodes 109 and 101 in the forward direction to inject charge into the active layer of 105, and carrier recombination light emission is amplified between the end faces of the resonator to cause laser emission. Light is emitted. In that case, 107 ZnSe layers are 1
It has a specific resistance of 0 MΩ · cm or more, and the injected current hardly flows except in the rib portion. Therefore, laser oscillation occurs only in the active layer just below the rib, and no unnecessary current flows, so that the threshold current decreases. The refractive index of the ZnSe layer is 2-53, which is smaller than that of the GaAs or AlGaAs layer of the active layer. Therefore, the effective refractive index of the portion immediately below the rib and the other portions are small on the outside, so that an optical confinement type optical waveguide is formed. As for the transverse mode of the oscillated light, only the fundamental transverse mode can be oscillated.

However, in order that only the fundamental transverse mode oscillates with a low threshold current, the astigmatic difference is small, and high-power laser oscillation is possible, the angle θ formed between the side surface of the rib and the joining plane is
There are certain restrictions on. FIG. 2 is a main cross-sectional view of a semiconductor laser according to an embodiment of the present invention, in which the angle indicated by the value of θ is indicated by 201. The values of the transverse mode characteristics, the threshold current, the astigmatic difference, and the maximum optical output in the case of various θ are summarized in the following table based on this embodiment.

As shown in the table, when the value of θ is smaller than 50 °, the oscillation threshold rises, and the maximum optical output decreases. Further, when the angle exceeds 120 °, higher-order mode oscillation is observed in the transverse mode, and the oscillated light is emitted as a plurality of spots. Therefore, the value of θ that has no practical problem is
50 ° to 120 °, more preferably 60 ° to 100 °
Is the range.

FIG. 3 is a diagram showing a manufacturing process of a semiconductor laser according to an embodiment of the present invention. 306 n-type GaAs buffer layer, 305 n-type AlGaAs clad layer, 304 GaAs or AlGaAs active layer, 303 P-type Al on n-type GaAs single crystal plate 301 by MOCVD
The GaAs clad layer and the P-type GaAs contact layer 302 are sequentially laminated, (FIG. 3B). Then, stripe-shaped ribs are formed by a normal photo process. (FIG. 3 (c)) Next, a ZnSe layer of 307 is embedded and grown again by the MOCVD method. (FIG. 3 (d)) Next, the ZnSe layer on the rib is etched again by a photo process. (FIG. 3 (e)) Next, a P-type ohmic electrode 308 and an n-type ohmic electrode 309 are formed to form a semiconductor laser. (FIG. 3 (f)) [Effects of the Invention] As described above, the present invention has the following effects.

(1) By optimizing the value of θ, the oscillation transverse mode is only the fundamental mode, and the light emission becomes a very beautiful spot.
Therefore, when the oscillated light is condensed by the lens system, it can be made into a minute spot of 1 μm or less, and a high SN ratio can be obtained at the time of reading of an optical information recording device such as a laser video disk or an optical memory.

(2) Further, by optimizing θ, laser oscillation light with an extremely small astigmatic difference can be obtained, and when incorporated in an optical head or the like, a complicated optical system required for shaping an outgoing beam or the like is not required.

(3) Further optimization of θ makes it possible to obtain a semiconductor laser having a low threshold current and a high output, and the reliability of the semiconductor laser is dramatically improved.

(4) Furthermore, the semiconductor layer that constitutes the semiconductor laser is MOCVD.
Since it is manufactured by the method, it is possible to form a semiconductor layer having a uniform property over a wide area, and it is possible to supply a semiconductor laser which is excellent in mass productivity and therefore low in cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a main sectional view showing an embodiment of a semiconductor laser of the present invention. FIG. 2 is a main sectional view showing an embodiment of the semiconductor laser of the present invention, and is a view showing θ. 3A to 3F are manufacturing process diagrams showing an embodiment of the semiconductor laser of the present invention. 101,309 …… n-type ohmic electrode 102,301 …… n-type GaAs single crystal substrate 103,306 …… n-type GaAs buffer layer 104,305 …… n-type AlGaAs clad layer 105,304 …… active layer 106,303 …… P-type AlGaAs clad layer 108,302 …… P-type GaAs contact layer 107,307 …… ZnSe buried layer 109,308 …… P-type ohmic electrode 201 …… Angle θ formed between the rib side surface and the junction plane

Claims (1)

[Claims] 1. A stripe-shaped rib is formed up to an intermediate depth of a cladding layer directly above the active layer of a double heterojunction semiconductor laser composed of an active layer and a cladding layer made of a III-V compound semiconductor. In a semiconductor laser in which both ends of the rib are filled with a semiconductor layer made of a II-VI group compound semiconductor, an angle (hereinafter referred to as θ) formed between a side surface of the rib and a bonding plane is 50 ° to 120 °. A semiconductor laser characterized in that there is.