JPS6355792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high power semiconductor laser.

Conventionally, there have been devices of this type as shown in FIGS. 1 and 2. The device shown in Figure 1 is called a buried hetero (BH) structure, where 1 is n-
GaAs layer, 2 is n-Al _x which constitutes the cladding layer
Ga _1-x As layer, 3 is n-Al _y constituting the optical waveguide layer
Ga _1-y As layer (y<x), 4 is the p-GaAs layer that constitutes the active layer, and 5 is the p-GaAs layer that constitutes the cladding layer.
Al _x Ga _1-x As layer, 6 is a high resistance Al _z Ga _1-z As that constitutes a cladding layer that laterally surrounds each layer 2 to 5.
layer (where z≧x). Figure 2 shows the strip
A cross-sectional view of the bellied hetero (SBH) structure, from 1 to
5 is the same as in Figure 1, and 7 is p-Al _z Ga _1-z
The As layer and 8 are n-Al _z Ga _1-z As layers.

Next, the operation will be explained. In FIG. 1, the current flowing from the cladding layer 5 is constricted by the high resistance layer 6 and is mainly injected into the active layer 4.
Here, radiative recombination occurs. The generated light is confined in the vicinity of the active layer 4 and the optical waveguide layer 3 by the surrounding cladding layers 2, 5 and 6, which are regions of low refractive index.

In the case of FIG. 2, the current flowing from the cladding layer 5 is constricted by the reverse biased layers 7 and 8 and is injected into the active layer 4. The light generated by radiative recombination is similarly confined by the surrounding low refractive index regions of each cladding layer 2, 5 and layer 7, but in this case, the optical waveguide layer 3 spreads laterally. Therefore, the light has a characteristic that it spreads more easily in the lateral direction than in the case of FIG.

In the above explanation, the magnitude relationship of the refractive index is
The refractive index of AlGaAs crystal is the Al mole fraction (x or y
or z) is based on the fact that it decreases as z) increases. That is, GaAs, Al _y Ga _1-y As, Al _x Ga _1-x As,
The refractive index decreases in the order of Al _z Ga _1-z As layers. (However, y<x≦z).

Since the conventional semiconductor laser is configured as described above, there is no optical waveguide region on the lateral (side) side of the active layer 4, and the effective refractive index in the lateral direction also changes stepwise, so that the optical The problem was that the lateral spread of the light was insufficient and the light emitting part was small, making it difficult to obtain high output.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by providing an optical waveguide layer with a gradually decreasing thickness next to the active layer,
The object of the present invention is to provide a semiconductor laser that can obtain high output by actively expanding the light emitting part in the lateral direction.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, numerals 1, 2, 4, 5 and 8 are exactly the same as in the conventional example described above. 9 is active layer 4
The p-Al _y Ga _1-y As constituting the optical waveguide layer whose thickness decreases as it moves away from the active layer 4 in the vicinity of
layer (0<y<x). This optical waveguide layer 9 can be easily produced by performing the second crystal growth to form the buried layers 8 and 9 using a liquid phase epitaxy (LPE) method. When a thin layer is grown by the LPE method on a substrate with "ridges" formed by etching layers 4 and 5, the first buried layer, which is the light guide layer, tends to grow on the sides of the "ridges". The wave layer 9 does not have a uniform thickness, but has a structure in which the "ridges" are raised. By appropriately selecting growth conditions such as temperature and time, the thickness distribution of the optical wave layer 9 can be controlled.

In the device constructed as described above, the optical waveguide layer 9 forms a reverse biased p-n junction with the layer 8, and the light flows from the cladding layer 5 as in the conventional example shown in FIG. It also plays the role of current constriction. Therefore, current mainly flows into the active layer 4, and light emission occurs there due to radiative recombination. However, the light leaks toward the optical waveguide layers 9 on both sides, resulting in a light-emitting portion that spreads in the lateral direction as a whole.
At this time, the refractive index distribution in the lateral direction does not change in a sudden step-like manner, but changes gradually, so the electric field strength distribution has a wider peak, that is, a shape close to a fishing pupil shape. Be expected. This is the same situation observed in the vertical direction in a structure in which waveguide layers are provided on both sides of an active layer in the vertical direction, a so-called separate confirmation heterojunction (SCH) structure. By realizing such an electric field intensity distribution, the proportion of high-intensity portions increases, high output can be achieved, and at the same time, the radiation angle of the beam can be narrowed.

In addition, in the above embodiments, n-
Although we have explained the case where GaAs is used as the substrate for molding, p-GaAs is used as the substrate, and the Al _y Ga _1-x As layer 2, the Al _x Ga _1-x As layer 3, and the Al _z Ga _1-z As layer 8 are formed. The same effect can be obtained even if the GaAs layer 4Al _x Ga _1-x As layer 5 and Al _y Ga _1-y As layer 9 are made of n-type while being made of p-type.

As described above, according to the present invention, an optical waveguide layer region whose thickness gradually decreases is provided on the sides of the active layer, and a portion of high light intensity is expanded in the lateral direction, so that high output can be obtained. This has the effect of reducing the spread of the beam in the lateral direction.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing a conventional semiconductor laser, and FIG. 3 is a cross-sectional view showing a semiconductor laser according to an embodiment of the present invention. In the figure, 2 is a first semiconductor layer, 9 is an optical waveguide layer, 4 is an active layer, and 8 is a second semiconductor layer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A first semiconductor layer of a first conductivity type, which is made of a material having a higher refractive index than the first semiconductor layer, and is provided on the first semiconductor layer so that the thickness becomes gradually thinner from one side to the other. a second conductivity type optical waveguide layer;
a second semiconductor layer of the first conductivity type, which is made of a substance having a lower refractive index than the optical waveguide layer and is provided on the optical waveguide layer; A semiconductor laser characterized in that only the active layer is provided adjacent to the optical waveguide layer.