JPS63179592A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser element having characteristics of quasi-zero-dimension electron state and high gain by forming an active layer of a step structure having a step in any direction in a plane. CONSTITUTION:A semiconductor laser element formed on a substrate 10 with a semiconductor laminated structure including an active layer 21 of light emitting region comprises a stepwise structure in the layer 21, and steps in any directions of perpendicular two directions in the plane. The layer 21 is formed thinly and the step interval of the structure is of 100Angstrom order or less in any two directions. Thus, the characteristics of quasi-zero-dimension electron state is remarkable, and a higher gain semiconductor laser element than that of the conventional one can be obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a semiconductor laser device.

(Prior Art) Semiconductor laser elements are key devices that determine the progress of optical fiber communication and optical information processing technology, and elements with large laser gain are required. The semiconductor laser is
This device has a layered structure on a semiconductor substrate in which the active layer is sandwiched between semiconductor layers with a wider forbidden band width than the active layer, and a current is injected into the electron units 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 has a cladding layer 11 . Active layer 12. A cladding layer 13 and a cap layer 14 are sequentially grown, and a current blocking structure 19 is formed by ion implantation. In order to increase the laser gain of a semiconductor laser, the property that the laser gain is larger in a two-dimensional electronic state than in a three-dimensional bulk electronic state is used. It is known that forming a thin active layer is effective.
Semiconductor lasers with such thin-film single-layer or multi-layer active layers are called quantum well lasers, and are currently being actively researched. On the other hand, if a thin line-like structure or dot-like structure with a size similar to the film thickness is formed in the direction parallel to the film,
Pseudo-one-dimensional and pseudo-zero-dimensional electronic states can be formed, respectively. In this case, the laser gain is even larger than in the case of a two-dimensional electronic state, and it is therefore possible to reduce the oscillation W4 current, reduce the temperature change of the flash current, and reduce the oscillation line width. has been shown theoretically. Applied Physics is also an attempt to actually form thin wire structures in semiconductors! , Tars (Appl, Phys, Let
t, 41.

635 (1982)), an attempt to form a dot-like structure in a semiconductor was also made by Petroff et al. in the Journal of Vacuum Science and Technology (J, Voc).
.

Sci, Technol, B4, 358 (
Reed (M, A. 1986) as described in
, Reed) et al. In these conventional attempts, the dimensions of the active layer can be sufficiently controlled in the film thickness direction using the molecular beam epitaxial (MBE) growth method, but in the in-plane direction of the active layer, fine line or dot-like patterns are formed using normal gluing method. The structure remained.

(Problems to be Solved by the Invention) As mentioned above, when trying to realize a quasi-zero-dimensional electronic state in the active layer, it is extremely difficult to form a dot-like pattern structure and control its dimensions using conventional lithography technology. was the problem. On the other hand, an element with a structure that can be made without relying on conventional lamination technology has not been known so far.

Furthermore, when a conventional dot-like pattern structure is applied to the active layer of a semiconductor laser device, light cannot be confined within the dot pattern, so light loss occurs in the no-gain region between the dot patterns. There was a growing problem.

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

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems is 'a semiconductor laser element in which a semiconductor laminated structure including an active layer, which is a light emitting region, is formed on a substrate. The active layer is characterized in that it has a step-like structure and has steps in both of two mutually orthogonal directions in the plane.

(Function) In the present invention, a semiconductor laser device having characteristics of a quasi-zero-dimensional electronic state is realized by the above-described means. In the structure of this invention, by reducing the thickness of the active layer and making the step interval of the staircase structure less than 100 people in both directions, the characteristics of the quasi-zero-dimensional electronic state are remarkable, and it is higher than that of the conventional structure. A semiconductor laser device with high gain can be obtained.

Embodiments of the present invention will be described in more detail below with reference to the drawings.

(Example) FIG. 1 is a schematic diagram of an element explaining an example of the present invention. FIG. 1(a) is a perspective view of the semiconductor laser device of the present invention. The features of the semiconductor laser device of the present invention are as shown in FIG.
) has a step-like active layer 21 as shown in the perspective view in Figure 2.Other features of the laser device structure are basically the same as the structure of the conventional semiconductor laser device whose schematic diagram is shown in Figure 2. It is. That is, a first cladding layer 11, an active layer 21 . It has a second cladding R13 and a cap layer 14.

The active layer 21 having a stepped structure as shown in FIG. 1(b) can be formed without relying on sophisticated lithographic techniques. below,
An example of its formation will be briefly described. First, a normal gallium arsenide substrate in which the axis 15 of the surface is inclined from the crystal axis [001] is prepared. The axis 15 of the substrate plane is tilted by an angle θ8 from the crystal axis [001] around one axis 16 of the shear plane,
Further, it is assumed that the crystal axis is rotated by an angle θ1 around the crystal axis [001].

In this embodiment, the axis 16 is the [110] axis, and the angles θ1 and θ are each approximately 2°. A cladding layer 11. is formed on such a substrate using, for example, an MBE growth method. active layer 21
．． Cladding layer 13. A cap layer 14 is epitaxially grown. At this time, the growth surface of the growth layer is as shown in FIG. 1(b).
It grows while maintaining a stair-like structure. Such a step-like growth phenomenon is well known as a step growth phenomenon, and is described, for example, in Applied Physics Letters (Ap.
pl, Phys.

Lett, 45, 620 (1984)), the present example also shows step growth in which the step difference is about 6 people and the step interval is about 160 people in both directions in the plane. confirmed.

The material composition in this embodiment is a normal one, and the aluminum composition ratio is about 0.00000 on the n-type gallium arsenide substrate 10.
n-type cladding layer 11 and p-type cladding layer 13.35 made of aluminum gallium arsenide. Undoped gallium arsenide active layer 21. A p-type gallium arsenide cap layer 14 was grown. Thereafter, a current blocking structure 19 was formed by ion implantation, and finally electrodes were provided on the top and bottom surfaces. In the semiconductor laser device fabricated in this way, compared to a normal quantum well laser device with the same active layer thickness and no stepped structure,
A favorable effect of improving laser characteristics was obtained by reducing the oscillation threshold current density. Also, the tilt angle θ1 from the substrate plane crystal axis.
θ, both 1°, 2. The above improvement effect increased as the step interval of the stairway structure was shortened by increasing the step distance to 3° and 3°.

In this example, we have described the case where the active layer consists of a single quantum well layer, but the contribution of the quasi-zero-dimensional effect is also expected when the active layer consists of a multi-layered multi-quantum well layer or a superlattice structure with electronic interaction between layers. The device having the structure of this example is effective. Furthermore, even if the thickness of the active layer is not as thin as in the case of a quantum well, the effect can be expected to some extent depending on the step size.In this example, an example of gallium arsenide-based MBE growth was described, but the method is similar to that of other organic metals. It can be easily inferred that it is effective for phase epitaxy (MOCVD) and normal vapor phase epitaxy (VPE), as well as for material systems such as indium phosphide gallium arsenide and indium gallium arsenide. Ru.

(Effects of the Invention) As explained above, the semiconductor laser device of the present invention has a step structure in which the active layer has steps in any direction in the plane, so that the two-dimensional electronic state characteristics of the same film thickness can be improved. It has a higher laser gain than conventional semiconductor quantum well lasers, and can be formed without special microfabrication processes, making it suitable for integrating optical devices and improving productivity. It can be used as a high-performance semiconductor laser device.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing one embodiment of the present invention;
b) is a perspective view showing the active layer in this embodiment, and FIG. 2 is a perspective view showing an example of a conventional semiconductor laser device. 10... Substrate, 11 River clad notification, 12... Active layer, 13... Clad layer, 14... Cap calendar, 15
... Axis of the substrate surface, 16 ... One axis of the arm opening surface, 19
... Current blocking structure, 21 ... Stepped active layer, θ1.
...The board surface inclination is the angle, θ, ...The board surface deviation angle.

Claims (1)

[Claims] In 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, the active layer has a step-like structure, and there are no steps in either of two orthogonal directions in the plane. A semiconductor laser device characterized by having: