JPH0638541B2 - Semiconductor laser device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor laser device.

(Prior Art) A semiconductor laser device is a key device that determines the progress in optical fiber communication and optical information processing technology, and a device having a large laser gain is required. The semiconductor laser is
An element in which an active layer has a layer structure sandwiched between semiconductor layers having a band gap wider than that of the active layer on a semiconductor substrate, and a current is injected into an electron unit in the active layer to accumulate carriers and emit laser light. . FIG. 2 is a perspective view showing an example of such a conventional semiconductor laser device. This device comprises a clad layer 11, an active layer 12, a clad layer 13 and a cap layer on a substrate 10.
14 are sequentially grown, and the current blocking structure 19 is formed by the ion implantation method. In order to increase the laser gain of a semiconductor laser, the property that the laser gain is larger in the two-dimensional electronic state than in the three-dimensional bulk electronic state is used so that the electrons in the active layer, which is the light emitting region, are quantized. It is known that it is effective to form an active layer having a thin film thickness. A semiconductor laser having such a thin-film single layer or multi-layer active layer is called a quantum well laser and is currently being actively studied. On the other hand, when a thin line-shaped structure or a dot-shaped structure having a size of the film thickness is formed in the direction parallel to the film, pseudo one-dimensional and pseudo zero-dimensional electronic states are formed, respectively. In this case, the laser gain becomes larger than that in the case of the two-dimensional electronic state, and therefore, there is a possibility that it is possible to reduce the oscillation threshold current, the temperature change of the threshold current, and the oscillation line width. Indicated In addition, an attempt to actually form a thin wire structure of a semiconductor is also performed by the Applied Physics Letters (App
l.Phys.Lett. 41, 635 (1982) by Petrov (Petroff) who as described in), also attempts dot-like structures formed of a semiconductor Journal of Vacuum Science and Technology ( J.Voc.Sci.Technol. B4 , 35
8 (1986)) by MA Reed et al. In these conventional trials, the thickness direction of the active layer is sufficiently controlled by using the molecular beam epitaxial (MBE) growth method, but the in-plane direction of the active layer is fine line or dot-shaped pattern by the ordinary lithography method. The structure was left behind.

(Problems to be Solved by the Invention) As described above, when it is attempted to realize a pseudo-zero-dimensional electronic state in the active layer, it is extremely difficult to form a dot-shaped pattern structure and control the dimensions by a conventional lithography technique. Was a problem. On the other hand, a device having a structure that can be realized without relying on the conventional lithography technique has not been known.

Furthermore, when the conventional dot-shaped pattern structure is applied to the active layer of the semiconductor laser device, the light cannot be completely confined within the dot pattern, so that there is no loss of light in the non-gain region existing between the dot patterns. There was an increasing problem.

The object of the present invention is to solve the problem of pattern formation,
It is an object of the present invention to provide a semiconductor laser device which has a problem of light loss and which has characteristics of a quasi-zero-dimensional electronic state and which has a higher gain than the conventional type.

(Means for Solving Problems) Means provided by the present invention for solving the above problems are semiconductor laser devices in which a semiconductor laminated structure including an active layer which is a light emitting region is formed on a substrate. In addition, the active layer has a stepwise structure and has a step in any of two in-plane orthogonal directions.

(Operation) In the present invention, the semiconductor laser device having the characteristics of the pseudo-zero-dimensional electronic state is realized by the above means. In the structure of the present invention, when the thickness of the active layer is thin and the step interval of the step structure is 100 Å or less in both directions, the characteristics of the pseudo-zero-dimensional electronic state are remarkable, and the gain is higher than that of the conventional type. The semiconductor laser device of

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

(Example) FIG. 1 is a schematic view of an element for explaining an example of the present invention. FIG. 1 (a) is a perspective view of a semiconductor laser device of the present invention. A feature of the semiconductor laser device of the present invention is that it has a stepwise active layer 21 as shown in a perspective view in FIG. The other features of the laser device structure are basically the same as the structure of the conventional semiconductor laser device shown in the schematic view of FIG. That is, the first clad layer 11, the active layer 21, the second clad layer 13, and the cap layer 14 are provided on the substrate 10.

The active layer 21 having a staircase structure as shown in FIG. 1 (b) can be formed without resorting to advanced lithography technology. Hereinafter, one example of the formation will be briefly described. First, a substrate is prepared in which the axis 15 of the surface of a normal gallium arsenide substrate is tilted from the crystal axis [001]. The substrate surface axis 15 is tilted from the crystal axis [001] about an axis 16 of the cleavage plane by an angle θ ₁ , and further rotated about the crystal axis [001] by an angle θ ₂ . In this embodiment, the axis 16 is the [110] axis, and the angles θ ₁ and θ ₂ are each about 2 °. The cladding layer 11, the active layer 21, the cladding layer 13, and the cap layer 14 are epitaxially grown on such a substrate by using, for example, the MBE growth method. At this time, the growth layer grows with the growth surface maintaining the staircase structure as shown in FIG. The phenomenon of such stepwise growth is well known as the step growth phenomenon, and for example, Applied Physics Letters (Appl. Phys. Lett. 45 , 620 (1984)).
It has been confirmed by the experiment described in. Also in this example, it was confirmed that the step growth was about 6 Å and the step interval was about 160 Å in both in-plane directions.

As the material composition in this embodiment, a usual material composition is adopted, and an n-type clad layer 11 and a p-type clad layer 13 made of aluminum gallium arsenide having an aluminum composition ratio of about 0.35 are formed on the n-type gallium arsenide substrate 10. Gallium arsenide active layer
21. A p-type gallium arsenide cap layer 14 was grown. After that, the current blocking structure 19 was formed by the ion implantation method, and finally the electrodes were provided on the upper surface and the lower surface. In the semiconductor laser device manufactured in this manner, a favorable effect of improving the laser characteristics in which the oscillation threshold current density is reduced is obtained as compared with the ordinary quantum well laser device having the same active layer thickness and no step structure. . Moreover, both the tilt angles θ ₁ and θ ₂ from the crystal axis of the substrate surface are 1 °,
The above-described improvement effect increased as the step interval of the staircase structure was shortened by sequentially increasing it to 2 ° and 3 °.

In this embodiment, the case where the active layer is composed of a single quantum well layer has been described, but the contribution of the pseudo-zero-dimensional effect is also expected when the active layer is composed of multiple quantum well layers or a superlattice structure with electron interaction between the eyebrows. Therefore, the device having the structure of this embodiment is effective. Even if the active layer is not as thin as the quantum well, the effect depending on the step size can be expected to some extent. In this embodiment, an example of MBE growth of gallium arsenide is described, but the method is also applicable to other metal organic chemical vapor deposition (MOCVD) and ordinary vapor phase epitaxy (VPE), and the material system is indium phosphide. It is easily inferred that it is effective for other systems such as gallium arsenide and indium gallium arsenide.

(Effect of the Invention) As described above, in the semiconductor laser device of the present invention, the characteristics of the two-dimensional electronic state of the same film thickness are obtained by forming the active layer into a step structure having a step in any in-plane direction. It has a higher laser gain than the conventional semiconductor quantum well laser, and there is a method that can be formed without performing a special microfabrication process. It can be used as a high performance semiconductor laser device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (a) is a perspective view showing an embodiment of the present invention, FIG. 1 (b) is a perspective view showing an active layer in this embodiment, and FIG.
FIG. 1 is a perspective view showing an example of a conventional semiconductor laser device. 10 …… Substrate, 11 …… Clad layer, 12 …… Active layer, 13 ……
Good layer, 14 ... Cap layer, 15 ... Substrate surface axis, 16 ...
… One axis of cleavage plane, 19… Current blocking structure, 21 …… Staircase active layer, θ ₁ …… Substrate tilt angle, θ ₂ …… Substrate misalignment angle.

Claims (1)

[Claims] 1. A semiconductor laser device in which a semiconductor laminated structure including an active layer which is a light emitting region is formed on a substrate, wherein the active layer has a stepwise structure and is in-plane orthogonal to each other.
A semiconductor laser device having a step in any direction.