JPS6342867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a new and useful technique regarding the device structure of a semiconductor laser device.

Semiconductor laser devices are generally based on light emitting diodes using direct transition materials such as GaAs, and various types such as homojunction, single heterojunction, and double heterojunction types are manufactured. There is. These semiconductor lasers constitute an optical resonator that performs multiple reflections, and by injecting sufficient carriers into this resonator to form a population inversion state, the conditions for stimulated emission are satisfied and laser oscillation is performed. be.

The optical eutectic is generally composed of a pair of crystal cleavage planes that are perpendicular to the pn junction plane and parallel to each other. When a forward voltage is applied to the p-n junction and a small number of electrons are injected across the p-n junction, they spontaneously (individually) recombine with holes and emit incoherent light. . When the current is increased, excited electron and hole pairs near the p-n junction recombine, and the light collides with other electron and hole pairs,
Because of that stimulation, the pair also recombines and emits light. That is, stimulated radiation begins to occur. Since the stimulated light travels in the same direction and in the same phase as the stimulated light, light amplification occurs through continuous repetition of this action. The p-n junction surface where the crystal is flat and the p-n junction surface as described above.
When composed of a pair of crystal cleavage planes that are perpendicular to the n-junction plane and parallel to each other, a portion of the light is reflected by the crystal cleavage planes that act as a semitransparent mirror and is further amplified. In other words, the light is repeatedly reflected using the crystal cleavage plane as the resonance plane, resulting in multiple reciprocating movements between the resonance planes. In this way, the light is confined between the two mirrors (resonant surfaces) and is repeatedly amplified by stimulated radiation. When the current is high enough, amplification occurs through stimulated radiation that overcomes absorption, scattering, leakage from the translucent mirror, and other losses, and at this point the amount of light trapped between the mirrors (resonant surfaces) is It increases rapidly and laser oscillation starts from the resonant surface.

Semiconductor laser oscillation requires a very high-density current, and in order to achieve continuous oscillation at room temperature, a double heterojunction type laser oscillation device in which the active region for laser oscillation is sandwiched between cladding layers has been implemented. In addition, various built-in refractive index waveguide structures have been proposed in order to perform fundamental transverse mode oscillation in conventional double heterojunction semiconductor lasers.

Figure 1 shows an example of this, the so-called
It is called CSP (Channeled Striped Planer) structure. This structure enables oscillation in the fundamental oscillation mode because oscillation light outside the groove (width W) is absorbed by the n-GaAs substrate 1, and the magnitude becomes larger as the higher-order mode increases. However, GaAs
The fundamental single mode is efficiently oscillated by the relationship among the thickness d of the active layer 3, the depth D and width W of the groove, and the thickness t of the n-Ga _1-x Al _x As cladding layer 2 outside the groove. has the following limitations:

(1) If d is made thinner in order to lower the oscillation starting current, the leakage of the fundamental mode will increase, and the absorption of the fundamental mode in the groove portion by the substrate will increase, so the depth D must be increased. As a result, the active layer 3 cannot be made flat unless the thickness of the layer other than the grooves is sufficiently increased due to constraints on growth conditions. Since t is set large, higher-order modes other than the grooves are not absorbed sufficiently by the substrate 1. Therefore, a stable fundamental mode cannot be obtained. From this, d, t, and D are uniquely determined.

(2) If W is narrowed in order to lower the oscillation starting current, the transverse fundamental mode will also be absorbed considerably, leading to a decrease in efficiency.

An object of the present invention is to provide a new and useful device structure for a semiconductor laser device to solve the above problems.

Hereinafter, one embodiment of the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram of the main parts of a semiconductor laser device showing one embodiment of the present invention.

A double-hetero junction type n-
Ga _1-x Al _x As clad layer 2, non-doped GaAs active layer 3, P-Ga _1-x Al _x As clad layer 4, n-
A GaAs layer 5 and a P-GaAs layer 6 are formed. Board 1
The groove formed in is a two-step groove with widths W and W'(W>W').

The n-clad layer 2 deposited on the GaAs substrate 1 is grown so as to completely fill the two-step trench and have a flat upper interface. Therefore, the active layer 3 grown thereon becomes a flat layer and has a uniform thickness. n-GaAs grown on p-clad layer 4
Since the layer 5 has the opposite polarity to the injected current, no current flows in this part, and the current is injected through the p-GaAs layer 6 located directly above the two-step groove, and the current flows mainly through the p-GaAs layer 6. Laser oscillation occurs in the region of the active layer 3 directly below the layer 6.

The thickness of the lower n-cladding layer 2 is set thin so that the higher-order mode light of the active layer is sufficiently absorbed into the substrate 1 in areas other than the two-step groove, and the width of the center part of the two-step groove is
The region W' is set to be sufficiently thick so that the transverse fundamental mode light of the active layer is not absorbed into the substrate.
Therefore, in the semiconductor laser device of this embodiment, stable laser oscillation in the transverse fundamental mode can be obtained with a low oscillation starting current.

The above configuration provides the following advantages.

(1) The volume of the groove can be reduced;
Even if the cladding layer 2 is made thinner, the active layer 3 can be grown evenly.

(2) Since the thickness t of the cladding layer 2 can be made thinner, higher-order modes can be sufficiently cut off.

(3) The basic mode can be made to receive less absorption.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional double heterojunction type semiconductor laser device. FIG. 2 is a block diagram of the main parts of a semiconductor laser device showing one embodiment of the present invention. 1...Substrate, 2...Clad layer, 3...Active layer.

Claims (1)

[Claims] 1 A two-step groove consisting of a first groove having a width W and a second groove having a width W′ (W′<W) along the center line of the first groove is formed on the crystal growth surface of the substrate. A lower cladding layer, a flat active layer having a uniform thickness, and an upper cladding layer are sequentially laminated on the crystal growth surface including the groove,
The layer thickness of the lower cladding layer is set to such a thickness that the higher-order mode light of the active layer is absorbed into the substrate in areas other than the two-step groove, and the lateral fundamental mode light of the active layer is absorbed in the second groove part. 1. A semiconductor laser device, wherein the thickness of the semiconductor laser element is set to such a thickness that it is not affected by the absorption effect of the substrate.