JPS61245592A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To enable high-output operation by forming sub-striped grooves while being adjoined on both sides of a main striped groove shaped to an active layer, curving and growing active layers in the grooves and thinly shaping an active layer on the main striped groove. CONSTITUTION:Striped grooves 22', 23' having a shape the same as or slightly larger than a main striped groove shaped in a post-process are formed to the growth surface of a P-type GaAs substrate 10, and an N-type GaAs current stopping layer 11 is grown on the substrate 10 so that a growth surface is flattened through a liquid-phase epitaxial growth method. A resist film 30 is formed onto the layer 11, and sub-striped grooves 22, 23 in a shape that they are overlapped to the mesa type striped grooves 22', 23' and a main striped groove 21 at the center of the grooves 22, 23 are shaped. The layer 30 is removed, and a P-GaAlAs clad layer 12, a GaAlAs active layer 13, an N-GaAlAs clad layer 14 and an N<+>-GaAs cap layer 15 are formed. The active layer 13 is curved in the sections of the grooves 22, 23, and the active layer 13 is thinned just above the main striped groove 21, thus acquiring a high output.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a technique for growing a thin active layer for laser oscillation in a well-controlled manner in a liquid phase epitaxial growth process in order to increase the output of a semiconductor laser.

<Conventional technology and its problems> As one of the means to achieve high output of semiconductor lasers,
A structure is known in which the active layer for laser oscillation is limited by a cladding layer, and the thickness of the active layer is made thin to allow light to seep into the cladding layer, thereby reducing the optical density within the active layer.

However, when crystal growth of a semiconductor laser device is performed using a liquid phase epitaxial growth method, it is considerably difficult to grow an epitaxial growth layer of 0.1 pmU or less with good controllability. The output intensity of the laser beam strongly depends on the thickness of the active layer, and as the active layer becomes thinner, the density of carriers confined within the active layer increases, creating a low current, high output laser oscillation state. In this case, by allowing the light from the active layer to seep into the cladding layer, destruction of the resonator end face due to optical power is prevented and stable high-output laser oscillation can be achieved for a long period of time.

In recent years, increasing the output power of laser light has become an essential element in order to effectively utilize semiconductor lasers in fields such as optical communication and information processing, and therefore it is possible to control the active layer to be thin and reproducible. Establishment of this technology is desperately needed.

Means for Solving the Problems> In view of the above problems, the present invention provides main stripe grooves adjacent to both sides of the main stripe grooves involved in laser oscillation, which are provided for current confinement in the active layer. By forming a sub-stripe groove having a stripe width wider than the stripe width of
We have established a semiconductor laser device capable of high output operation, which is characterized by setting the active layer thickness in this part thin by utilizing the effect of controlling the growth rate of the active layer directly above the main stripe groove sandwiched by this curved part. It is something.

<Example> Refer to FIG. 1) to (El [FIG. 1] A manufacturing process diagram of a semiconductor laser device showing an example of the present invention.

As shown in Figure 1 (Al), the grooves have the same shape as the main stripe grooves to be formed in the later process on the growth surface of the P-type GaAs substrate (Zn doped: carrier concentration lXl019fl'') 10, or are slightly thicker than the main stripe grooves. b Stripe grooves 22' and 23' are formed.In this example, the mesa-shaped stripe grooves 22' and 23' are 8 μm wide and 1 μm deep, and 40 mm are formed by etching.
Two trees were formed at μm intervals3). Subsequently, an N-type GaAs current blocking layer (Te doped: 6X] O"cyn-3) was formed on the GaAs substrate by epitaxial growth on the liquid, as shown in Fig. 1).
Mesa type stripe grooves 22 are formed so that 11 is completely buried in mesa type stripe grooves 22' and 23' and the growth surface is flat.
Epitaxial growth is performed so that the layer thickness at positions other than ', 23' becomes 0.8 μm. This current blocking layer 11 is set to have a conductivity type opposite to the injected current. Thereafter, a resist film 30 is formed on the surface of the current blocking layer 11, overlapping the mesa-shaped stripe grooves 22' and 23' and at the center position between the 8 μm wide sub-stripe grooves 22.23 and the sub-stripe grooves 22.23. In order to form the main stripe grooves 21 with a width of 3 μm, the resist film 30 is etched to form striped holes 31, 32, and 33 as shown in FIG. 1C1. Next, by etching, as shown in FIG.
2.23 is formed to have a depth of 1 μm. Since the layer 11 constituting the growth substrate has grown thick in this manner, no current flows in this portion. On the other hand, the main stripe groove 21
is formed as a groove with a V-shaped cross section by etching to a depth of 1 μm, and since the bottom of the groove reaches the P-GaAs substrate 1O, the current blocking layer 11 is removed at the bottom of the groove, and this part A current path is opened. The current path is formed only in the main stripe groove 21 that is involved in light emission.
This has the effect of reducing the amount of current loss that is not involved. Thereafter, the resist film 30 is removed and a P-G a Aji+ As cladding layer 12 is grown again by liquid phase epitaxial growth to form a heterojunction with the active layer as shown in FIG. 1(E). GaAaAs active layer 13 which becomes a resonator for laser oscillation. An n-GaAfflAs cladding layer 14 for forming a heterojunction and an n''-GaAs cap layer 15 for making ohmic contact with an electrode are sequentially grown to form a multilayer crystal for laser operation with a double heterojunction structure.

During this growth, the width of the sub-stripe grooves 22 and 23 is wider than that of the main stripe groove 21.

The p-cladding layer 12 that is formed first has a concave shape that is curved downward at the sub-stripe grooves 22 and 23 due to the influence of the underlying layer shape. When the active layer 13 is grown on this cladding layer 12, the growth rate of the active layer 13 in the curved part of the cladding layer 12 is faster than that in the flat part of the cladding layer 12, so the cladding layer ] The As in the growing melt that is in contact with the curved part 2 is quickly consumed and As diffuses around the melt. As a result,
Since the As concentration around the curved portion is reduced, the growth rate of the active layer 13 grown from the flat portion around the curved portion is suppressed. In this embodiment, the sub stripe groove 22
．． Since the curved active layer is formed to be thick just above 23, the growth rate around it, especially right above the main stripe groove 21 between the two sub-stripe grooves 22 and 23, is suppressed.

By suppressing the growth rate of the active layer 13 in this way, a thin active layer 13 can be easily obtained, and controllability and reproducibility of the active layer thickness can be ensured.

The thickness of the p-cladding layer 12 is controlled to be so thin that a portion of the light in the active layer 13 is absorbed toward the substrate 10 side.

FIG. 2 shows the main stripe groove 21 obtained by the above embodiment.
The main stripe groove 21 and the sub-stripe groove 22 of the semiconductor laser device have a stripe width of 3 μm, a stripe width of the sub-stripe grooves 22.23 of 8 μm, and a depth of both 1 μm.
．． 23 illustrates the effect of reducing the active layer thickness by slowing down the elongation speed when changing the spacing between 23 and 23. The growth conditions were a supersaturation degree of 4° C. and an active layer growth time of 2 seconds. Assuming that the distance between the main stripe groove 21 and one of the sub-stripe grooves 22 and 23 is W, the shorter W is, the more effective it is in thinning the active layer even when the active layer is grown by liquid phase epitaxial growth under the same conditions. It is recognized that when W increases to a certain extent (approximately 70 μrn), the effect of the sub-stripe grooves 22 and 23 disappears.

P and n side electrodes are formed on the double heterojunction structure multilayer crystal produced as described above by a method similar to the conventional method, and a laser oscillation resonator is formed by two folds, and the crystal is divided into individual laser elements. This laser element has a 2~
Three times higher output operation is now possible with 23 sub-stripe grooves. - Incidentally, in the above embodiment, the sub stripe grooves may be provided only on one side of the main stripe groove, or may be formed in plural on each of the left and right sides. Also, as a laser element, GaAJA
In addition to s-based materials, GaAfflInP-based materials and other various materials can be used.

<Effects of the Invention> As described in detail above, according to the present invention, a thin active layer can be formed with good controllability, so that it can be effectively used in various fields as a high-output semiconductor laser device.

[Brief explanation of drawings]

Fig. 1 A) to (F, l are explanatory diagrams of the manufacturing process of a semiconductor laser device showing one embodiment of the present invention. To Fig. 2 + [B) rri FIG. 2 is a perspective view of a semiconductor laser device and an explanatory diagram showing the relationship between stripe groove interval W and active layer thickness. DESCRIPTION OF SYMBOLS 10... Substrate, 11... Current blocking layer, 12... p
-Representative Patent Attorney Aihiko Fukushi (and 2 others)

Claims (1)

[Claims] 1. Forming stripe grooves along the stripe structure that curves the active layer at left and right positions of the current confinement stripe structure with respect to the active layer for laser oscillation, and forming stripe grooves along the stripe structure that curve the active layer, and forming stripe grooves around the curved portions of the active layer directly above the stripe grooves. A semiconductor laser device characterized in that the active layer is formed in a thin layer directly above the stripe structure.