JPH0545076B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a distributed reflection semiconductor laser used as a light source for optical communication, and a manufacturing method.

"Conventional technology" Recently, as a type of distributed reflection semiconductor laser,
A new type of semiconductor laser called a BIG (Bundled Integrated Guides) laser has been developed. FIG. 4 is a cross-sectional perspective view showing an example of the configuration of this BIG laser. In the figure, 1 is a p-InP substrate, 2 is a p-InP buffer layer, and 3 is λg = 1.55 μm
InGaAsP active waveguide layer, 4 is λg = 1.0 ~ 1.2 μm
5 is an n-InGaAsP (or n-InP) protective layer, 5 is an n-InGaAsP outer waveguide layer with λg = 1.3 to 1.4 μm,
6 is n-InP cladding layer, 7 is SiO ₂ insulating film, 8 is
a and 8b are metal electrodes, 9 is a window for the metal electrode 8a, 10 is a distributed black reflector (diffraction grating), and 11 to 13 are n which respectively constitute a buried layer.
-InP layer, P-InP and n-InGaAsP.
Moreover, X shown in the figure is an active region, and Ya and Yb are external waveguide regions.

In the above configuration, ns: p-InP substrate 1 and n-InP cladding layer 6
refractive index nact: refractive index of active waveguide layer 3 ncov: refractive index of protective layer 4 next: refractive index of outer waveguide layer 5 tact: thickness of active waveguide layer 3 tacv: thickness of protective layer 4 text : When the thickness of the external waveguide layer 5 is set, tact>next>ncov≧...(1), and under this condition, the material composition and thicknesses tact, tcov, and text of each layer are By setting it appropriately, it is possible to match the propagation constant and electric field distribution. According to the experimental results, the coupling efficiency between the active waveguide layer 3 and the external waveguide layer 5 could be set to a value of 90% or more and close to 100%.

As described above, according to the configuration shown in FIG. 4, the coupling between the active waveguide layer 3 and the external waveguide layer 5 can be achieved extremely well, so that the occurrence of reflection, scattering, etc. can be almost eliminated. As a result, highly efficient and highly stable single mode laser oscillation can be performed. Note that even if the conductivity (p-type and n-type) of each layer is reversed in the configuration shown in FIG. 4, exactly the same effect can be obtained. However, in this case, a cap layer and a Zn diffusion region are required.

"Problems to be Solved by the Invention" By the way, in the above-mentioned BIG laser, a part of the current injected from the electrode 8b flows into the active waveguide layer 3, as shown by arrow A1 in FIG. It is not injected and instead flows as a leakage current through the external waveguide region Ya3Yb, resulting in the problem that the threshold current is not reduced.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a distributed reflection semiconductor laser that can significantly reduce the leakage current flowing through the external waveguide region.

"Means for Solving the Problems" The present invention provides a means for solving the problem between an external waveguide layer excluding the portion above the active waveguide layer (i.e., an external waveguide layer in the external waveguide regions Ya and Yb) and a semiconductor substrate. It is characterized in that a first semiconductor layer of a conductivity type opposite to that of the semiconductor substrate and a second semiconductor layer of the same conductivity type as the semiconductor substrate are sequentially laminated.

"Function" The first and second semiconductor layers have p-
An n-inverse junction is formed, which prevents leakage current through the outer waveguide region.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a distributed reflection semiconductor laser (BIG laser) according to an embodiment of the present invention, and in this figure, parts corresponding to those in FIG. 4 are given the same reference numerals. In this figure, 1 is a p-InP substrate, and on this substrate 1, an n-InP first semiconductor layer 15 of the opposite conductivity type as the substrate 1, and a p-InP second semiconductor layer of the same conductivity type as the substrate 1. The active waveguide layer 3 and the external waveguide layer 5 are formed on the second semiconductor layer 16. However, in this case, the first semiconductor layer 15 is
It is not formed below the active waveguide layer 3. 1
0 is a distributed Bragg reflector provided along the outer waveguide layer 5, 4 is a protective layer formed on the active waveguide layer 3, 6 is a cladding layer formed on the outer waveguide layer 5, 7 is a SiO ₂ film, and 8a and 8b are electrodes.

Note that the semiconductor laser according to this example has a fourth
Similar to the one shown in the figure, it has an embedded structure.

Next, a method for manufacturing the above-mentioned semiconductor laser will be explained.

First, as shown in FIG. 2A, a first semiconductor layer 15 is grown on a substrate 1 by a liquid phase epitaxial method.

Next, as shown in FIG. 2B, a portion of the first semiconductor layer 15 corresponding to the active conductive layer 3 is removed by etching using photolithography.

Next, a second growth is performed, and as shown in FIG. 2C, the second semiconductor layer 16, the active waveguide layer 3, and the protective layer 4 are sequentially grown in a liquid phase.

Next, as shown in FIG. 2D, the active waveguide layer 3 and the protective layer 4 are formed by photolithography.
Remove the left and right sides in the figure.

Next, the second
As shown in FIG. 2E, a distributed Bragg reflector 10 is formed on the upper surface of the semiconductor layer 16 by photolithography.

Next, a third growth is performed, and as shown in FIG. 2, the external waveguide layer 5 and the cladding layer 6 are grown in a liquid phase.

Next, similar to the conventional structure, after forming a mesa stripe structure, a buried layer is formed by liquid phase growth (see buried layers 11 to 13 in FIG. 4), and then a SiO ₂ film 7 is formed. , forming electrodes 8a and 8b.

The above is the manufacturing method of the embodiment shown in FIG. 1, but the following method may also be used.

First, as shown in FIG. 3A, recesses 1a, 1b, . . . are formed in the substrate 1 by photolithography.

Next, as shown in FIG. 3B, the n-InP layer 1
5a is subjected to liquid phase growth.

Next, remove the upper part of the one shown in Figure 3 (C) using a melt bag, and remove the upper part of the one shown in Figure 3 (C).
A semiconductor layer 15 is formed.

The following steps are the same as in the case of FIG.

Therefore, in the case of the method shown in Fig. 2, the number of growth steps is increased by one compared to the case of manufacturing the conventional product shown in Fig. 4, but in the case of the method shown in Fig. 3, the meltback can be effectively Through control, it is possible to manufacture without increasing the number of growth steps.

"Effects of the Invention" As explained above, according to the present invention, there is a gap between the external waveguide layer excluding the portion on the active waveguide layer (that is, the external waveguide layer in the external waveguide region) and the semiconductor substrate. A first semiconductor layer of the opposite conductivity type to the semiconductor substrate and a second semiconductor layer of the same conductivity type as the semiconductor substrate were sequentially laminated.
A p-n inverse junction for the injection current is formed in the outer waveguide region by the semiconductor layer of
Leakage current passing through the external waveguide region can be reduced to almost zero. As a result, a highly reliable distributed reflection semiconductor laser with a small threshold current can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of the present invention, FIG. 2 is a process diagram for explaining the manufacturing method of the same embodiment, and FIG. 3 is a diagram for explaining another manufacturing method of the same embodiment. FIG. 4 is a cross-sectional perspective view showing a configuration example of a conventional distributed reflection type semiconductor laser (BIG laser), and FIG. 5 is a cross-sectional view for explaining the problems of the conventional example. 1... Semiconductor substrate, 3... Active waveguide layer, 4...
...protective layer, 5...outer waveguide layer, 10...distributed Bragg reflector, 15...first semiconductor layer, 16...
Second semiconductor layer.

Claims (1)

[Claims] 1. A semiconductor substrate, an active waveguide layer formed in a predetermined region on this semiconductor substrate, a protective layer laminated on this active waveguide layer, and In a distributed reflection semiconductor laser having an external waveguide layer formed so as to surround each of these layers in contact with each other, and a distributed Bragg reflector provided along a predetermined portion of the external waveguide layer, the active waveguide layer A first semiconductor layer of an opposite conductivity type to the semiconductor substrate and a second semiconductor layer of the same conductivity type as the semiconductor substrate are sequentially laminated between the external waveguide layer and the semiconductor substrate except for the upper part. Distributed reflection semiconductor laser.