WINDOW VSIS SEMICONDUCTOR LASER

Abstract: A window VSIS semiconductor laser includes a stimulated region and window regions formed on both ends of the stimulated region. A V-shaped groove is formed in a substrate, and an active layer is formed on the substrate. In one preferred form, the V-shaped groove has a wider width in the stimulated region as compared with the V-shaped groove formed in the window regions. The active layer is a crescent active layer in the stimulated region. One edge of the V-shaped groove in the stimulated region is continuously aligned on a line to the corresponding edge of the V-shaped groove formed in the window regions so as to enhance the optical coupling. In another preferred form, indents are formed in the substrate in the window regions in a manner to sandwich the V-shaped groove formed in the window regions. The V-­ shaped groove has the same width in the stimulated region and in the window regions. The active layer is plane shaped in the stimulated region, and a thickness of the active layer in the stimulated region is thicker than the active layer formed in the window regions.

Description: The present invention relates to a window V-channeled substrate inner stripe (referred to as VSIS hereinafter) laser. A paper entitled "Visible GaAlAs V-Channeled Substrate Inner Stripe Laser With Stabilised Mode Using p-GaAs Substrate" appearing in Applied Physics Letter, Vol.40, no. 5, March 1982, pages 372-374, AIP, New York, US, by S. Yamamoto et. al. describes a laser of this kind, in which the current is perfectly confined in the V-channel by the inner stripe, and fundamental transverse and single longitudinal mode operation is obtained because the built-in optical waveguide is formed within the V-channel. This laser structure does not have window regions. A window VSIS laser is proposed in, for example, our published European Patent Application No. 0095826. The conventional window VSIS laser does not show a smooth mode conversion between the window region having a plane active layer, and a stimulated region having a crescent active layer. Therefore, the operational mode is not stable at a high power operation. Furthermore, it is difficult to accurately control the manufacture of the crescent active layer in the normal liquid phase epitaxial method. Accordingly, the present invention aims to provide a semiconductor laser which provides a stable operation even at a high power operation, and even when the ambient temperature varies. It also aims to provide a novel window VSIS semiconductor laser structure, which ensures stable manufacturing. According to the present invention, there is provided a window V-channeled substrate inner stripe (VSIS) semiconductor laser having a stimulated region and respective window regions formed at opposite ends of said stimulated region, comprising: a substrate; a V-shaped groove formed in said substrate; and an active layer formed on said substrate above the groove characterised in that said V-shaped groove has the same width in said stimulated region and in said window regions, the edges of said V-shaped groove being aligned in said stimulated and window regions, and in that said substrate includes indents formed in said window regions so as to sandwich said V-shaped groove formed in each of said window regions, said active layer being thicker in said stimulated region than in said window regions. The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: Figure 1 is a plan view of the conventional window VSIS semiconductor laser; Figure 2 is a sectional view taken along line II-II of Figure 1; Figure 3 is a sectional view taken along line III-III of Figure 1; Figure 4 is a plan view of a window VSIS semiconductor laser according to the invention disclosed and claimed in copending published European patent application No. 0155853 from which this present application is divided; Figure 5 is a graph showing the laser wavelength which varies depending on the operating temperature, in the conventional window VSIS semiconductor laser of Figure 1 and in the window VSIS semiconductor laser of Figure 4; Figure 6 is a plan view of an embodiment of a window VSIS semiconductor laser of the present invention; Figure 7 is a sectional view taken along line VII-VII of Figure 6; and Figure 8 is a sectional view taken along line VIII-VIII of Figure 6. In order to facilitate an understanding of the present invention, an example of the conventional window VSIS semiconductor laser will be first described with reference to Figures 1, 2 and 3. The window VSIS semiconductor laser of Figures 1, 2 and 3 has the same structure as that disclosed in the copending published European Patent Application No. 0095826. Figure 1 is a plan view of the conventional window VSIS semiconductor laser. Figure 2 shows the structure at the stimulated region, and Figure 3 shows the structure at the window region. The stripe width W c1 of a V-shaped groove at a stimulated region 11 is greater the the stripe width W c2 of the V-shaped groove in window regions 12. By this structure, an active layer 17 in the stimulated region has the crescent configuration, and the active layer 17 at the window region has the plane configuration. Further, the active layer 17 in the stimulated region is thicker than the active layer 17 in the window region. The thus formed window VSIS semiconductor laser shows the laser emission at the wavelength of 780 nm and at the output power below 120 mW at which the thermal saturation occurs. Further, the window VSIS semiconductor laser of Figure 1 shows a stable fundamental transverse mode below the output power of 60 mW. In the conventional window VSIS semiconductor laser, the V-shaped groove is not continuous at a boundary 13 provided between the stimulated region 11 and the window region 12. Therefore, the laser beam is reflected at the boundary 13. That is, a smooth mode conversion is not achieved between the stimulated region 11 and the window region 12. This precludes a stable operation at a high power output operation. In the structure of the window VSIS semiconductor laser shown in Figure 4 according to the invention of application no. 0155853, the stimulated region (taken along line II'-II') has the similar sectional structure as that disclosed in Figure 2, and the window region (taken along line III'-III') has the similar sectional structure as that disclosed in Figure 3. A V-shaped groove C₁ in the stimulated region 11 has a width W c1 which is wider than a width W c2 of a V-shaped groove C₂ in the window regions 12. One edge of the V-shaped groove C₁ in the stimulated region is formed at a position where the edge is aligned on the same line with respect to one edge of the V-shaped groove C₂ formed in the window region 12. Since the stripe width W c1 is wider than the stripe width W c2 , the remaining edge forms discontinuous boundaries 20 between the stimulated region 11 and the window regions 12. Reference numeral 21 refers to a boundary formed between the stimulated region and the window region at the side where the groove edges are aligned, where the waveguide g₁ of the stimulated region is displaced with respect to the waveguide g₂ of the window region. The reader is referred to published application no. 0155853 for a description of the manufacturing steps and for preferred dimensions of the window VSIS semiconductor laser of Figure 4. In the Figure 4 structure, since the one edge of the V-shaped groove is formed continuously between the stimulated region and the window regions, a smooth optical coupling is ensured. A stable oscillation in the fundamental mode is conducted even at a high power output. More specifically, the laser emission in the fundamental mode is ensured at the output of 120 mW. The waveguides g₁ and g₂ are slightly discontinuous between the stimulated region and the window regions as shown in Figure 4. Accordingly, the window VSIS semiconductor laser of Figure 4 functions as the inner interface type. Therefore, the transverse mode is very stable. Figure 5 shows the variation of the laser wavelength depending on the temperature variation. The curve A shows the wavelength variation in the window VSIS semiconductor laser of Figure 4. The wavelength varies at the rate of 0.6Å/°C (1Å = 0.1 nm) when the operating temperature changes from 0°C to 60°C. The curve B shows the wavelength variation in the conventional window VSIS semiconductor laser shown in Figure 1, wherein the wavelength varies at the rate of 3Å/°C. The window VSIS semiconductor laser of Figure 4 includes a crescent active layer as shown in Figure 2. It is difficult to properly control the crescent configuration of the active layer, and Figure 6 shows an embodiment of the window VSIS semiconductor laser of the present invention, which includes a plane active layer even in the stimulated region, and the V-shaped groove is formed continuously between the stimulated region and the window regions. Figure 7 shows the sectional structure of the stimulated region, and Figure 8 shows the sectional structure of the window region. Indents 30 are formed in a substrate 32 at the window regions so as to sandwich a V-shaped groove 34. Because of the indents 30, the thickness T A of an active layer 36 in the stimulated region is greater than the thickness T B of the active layer 36 in the window regions. The V-shaped groove 34 has the same width in the stimulated region and in the window regions, and the active layer 36 in the stimulated region has a plane configuration. In a preferred form, the substrate 32 includes a p-GaAs first layer 320 (Zn-doped concentration 1 x 10⁻¹⁹cm⁻³), and an n-GaAs second layer 322 (Te-doped concentration 6 x 10⁻¹⁸cm⁻³) formed by the liquid phase epitaxial method. A p-Ga 0.5 Al 0.5 As cladding layer 38 is formed on the n-GaAs second layer 322, the p-Ga 0.5 Al 0.15 As active layer 36 is formed on the cladding layer 38, an n-Ga 0.5 Al 0.5 As cladding layer 40 is formed on the active layer 36, and an n-GaAs cap layer 42 is formed on the cladding layer 40. The manufacturing steps are as follows. The n-GaAs second layer 322 preferably has a thickness of about 1.0 micron. A resist film is deposited on the substrate 32 to cover the n-GaAs second layer 322 except the V-shaped groove portion. The etching operation is carried out into the n-GaAs second layer 322 to the depth of about 0.7 microns. Then, the resist film is removed at the indent portions, and the etching operation is carried out into the n-GaAs second layer 322 to the depth of about 0.5 microns. With this sequential etching, the V-shaped groove has the depth of about 1.2 microns, and the V-shaped groove 34 reaches the p-GaAs first layer 320 so as to form the current path. In a preferred form, the stimulated region has a length of about 150 microns, and each of the window regions has a length of about 50 microns. While the active layer 36 is formed by the liquid phase epitaxial method, arsenic (As) included in the gallium (Ga) solution is used to bury the indents 30 in the window regions. The epitaxial growth of the active layer 36 in the window regions is slower than that in the stimulated region and, therefore, the thickness T B of the active layer 36 in the window regions becomes thinner than the thickness T A of the active layer 36 in the stimulated region. In a preferred form, the thickness T A of the active layer 36 in the stimulated region is about 0.2 microns, and the thickness T B of the active layer 36 in the window regions is about 0.1 microns. Since the window regions have the thinner active layer, the laser beam emitted in the stimulated region is not absorbed in the window regions. The V-shaped groove is continuous between the stimulated region and the window regions. Further, the stimulated region includes the plane active layer. The invention being thus described, it will be obvious that the same may be varied in many ways without departure from the scope of the invention, which is limited only by the following claims.

Claims: A window V-channeled substrate inner stripe (VSIS) semiconductor laser having a stimulated region and respective window regions formed at opposite ends of said stimulated region, comprising: a substrate (32); a V-shaped groove (34) formed in said substrate; and an active layer (36) formed on said substrate above the groove (32) characterised in that said V-shaped groove (34) has the same width in said stimulated region and in said window regions, the edges of said V-shaped groove being aligned in said stimulated and window regions, and in that said substrate (32) includes indents (30) formed in said window regions so as to sandwich said V-shaped groove formed in each of said window regions, said active layer (36) being thicker in said stimulated region than in said window regions. A window VSIS semiconductor laser according to claim 1 wherein said active layer (36) has a plane configuration in said window and stimulated regions over said V-shaped groove (34). A window VSIS semiconductor laser according to claim 1 or claim 2 wherein said substrate (32) comprises a first base layer (320) and a second layer (322) formed in said first base layer (320), said V-shaped groove being formed in said second layer so as to reach said first base layer (320).

Inventors: HAYASHI, HIROSHI, MORIMOTO, TAIJI, YAMAMOTO, SABURO, YANO, SEIKI
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1985
Main classification: H01S3
IPC codes: H01S5