JPH01295471A - Photo-semiconductor element - Google Patents

Abstract

PURPOSE:To increase light output, by a method wherein a first light guide layer, a depletion layer and an active light guide layer, whose refractive indexes are different, are laminated in order on a upper surface of a semiconductor substrate on which a diffraction grating is formed, and, after a part of depletion layer and a part of the active light guide layer are eliminated, a second light guide layer and a clad layer are laminated in order on the upper surface of a wafer. CONSTITUTION:On a semiconductor substrate 10, on which a diffraction grating is formed, the following are laminated in order; a first light guide layer 12, a depletion layer 13 whose refractive index is smaller than that of the layer 12, and an active light guide layer 14 whose refractive index is larger than that of the layer 12. After a part of the depletion layer 13 and a part of the active light guide layer 14 are eliminated, the following are laminated in order, on the whole part of the upper surface of a wafer; a second light guide layer 15 having the same composition as the first light guide layer 12, and a clad layer 16 having the same refractive index as the semiconductor substrate 10. Thereby, unevenness of the diffraction grating does not vanish in high temperature standby state, thereby high output can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical semiconductor element used as a light source for optical communications.

"Prior Art" Semiconductor lasers are conventionally known as optical semiconductor devices used as light sources for optical communication, and in particular, semiconductor lasers have a diameter of 1.55 μm4
DI as a light source for optical communications? 13 (distributed reflection type) laser and DBR (distributed feedback type) laser are known.

These DPB lasers and D B It lasers are both lasers that oscillate in a dynamic single mode, and the DF laser has a diffraction grating formed above or below the active waveguide layer.
A BR laser has a diffraction grating formed in a low loss waveguide layer coupled to one or both ends of an active waveguide layer. However, although the optical output of the DP laser is quite large, it oscillates in two modes in principle, so it is necessary to provide a phase shift region of λ/4 in the middle of the waveguide, which complicates the process.

On the other hand, in principle, the D-mouth R laser oscillates in the cross-mode, but with the current technology, the DI? The optical output cannot be expected to be as high as that of the B laser.

By the way, in recent years, Professor Suematsu of Tokyo Institute of Technology and others have
DI? The DrL (D1aLributod-
IN eflecLor) laser has also been developed.

A cross section of this laser is shown in FIG. In this figure, ■
is a substrate, 2 is a buffer layer, 3 is a 1.55 μl active waveguide layer, 4 is a depression layer, 5 is a 1.3 μm external waveguide layer, 6 is a diffraction grating formed on the top surface of the external waveguide ff5, and 7 is a The region that is the cladding layer and includes the active waveguide layer 3 is DI? B, other areas are DBrt.

Further, the coupling structure between the active waveguide layer 3 and the outer waveguide layer 5 is B I G (Bundle Integra
ted Guide) structure. Therefore, this DR laser oscillates at high output due to the DF [(structure), and the light that leaks from the active waveguide layer 3 to the external waveguide H5 side is reflected by the highly wavelength selective reflector of the DBR structure. Feedback is efficient and high output can be obtained.

"Problems to be Solved by the Invention" However, the above-mentioned DI't laser is
Since the diffraction grating is formed on the external waveguide layer 5 made of sP, when the cladding layer 6 made of InP is grown on it, the wafer is not brought back in the high temperature state before growth. During this time, the unevenness of the diffraction grating disappears. As a result, the reflectance or feedback rate becomes low, making it difficult to obtain an element with a large optical output. In addition, the number of times of crystal growth in the manufacturing process is four times, including the crystal growth for forming the final buried structure, and there is also the drawback that it is difficult to control the dopant.

The present invention has been made in view of the above-mentioned circumstances, and aims to provide an optical semiconductor element that can obtain high output and reduce the number of times of crystal growth during manufacturing.

"Means for Solving the Problems" The present invention provides a first optical waveguide layer on a semiconductor substrate having a diffraction grating formed on the upper surface, a depletion layer having a refractive index smaller than the first optical waveguide layer, and the first optical waveguide layer. After sequentially laminating active waveguide layers having a higher refractive index than the first optical waveguide layer and removing a portion of the depletion layer and the active waveguide layer, a second optical waveguide layer having the same composition as the first optical waveguide layer is formed on the entire upper surface of the wafer. It is formed by sequentially laminating layers and a Crabstone layer having the same refractive index as the semiconductor substrate.

"Function" According to the present invention, since the diffraction grating is formed on the semiconductor substrate, the unevenness of the diffraction grating does not disappear during high temperature standby before growing the semiconductor layer on the diffraction grating. The number of times of crystal growth can be reduced.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the structure of a semiconductor laser according to an embodiment of the present invention. The semiconductor laser shown in this figure is different from the conventional one shown in FIG.
is formed on the upper surface of the semiconductor substrate 10.

A method of manufacturing this semiconductor laser will be described below.

(2) An I-order diffraction grating II is formed on the upper surface of the p-1nP substrate 10 by etching.

■Substrate with diffraction grating 1.1 formed! On the top surface of O, p-
1nGaAgP number! The optical waveguide layer 12, the p-NP dipleg layer 13, and the undoped InGaAsP active waveguide layer 14 (λ9=1.55 μ−) are epitaxially grown (first growth).

(2) Part of the active waveguide layer I4 and depletion layer 13 (the right half in the figure) is removed by selective etching.

■N-1nG on the top surface of the wafer after the process of ■ above.
The aA sP second optical waveguide layer +5 and the n-1nP cladding layer 1G are sequentially grown (second growth).

■Form an embedded structure in which the waveguide layer is embedded. That is,
After the side portions of the waveguide layers 12 to 15 (the side portions on the front side of the paper and the side portions on the back side of the paper) are removed by etching, a current blocking layer is grown in those portions (third growth).

The above is the manufacturing process of the semiconductor laser shown in FIG. As described above, according to the structure shown in FIG. 1, epitaxial growth, which conventionally required four times, can be performed only three times. Furthermore, since the diffraction grating is formed on the InP, the unevenness does not disappear during high temperature standby before the next growth.

In addition to the above-described embodiments, a structure in which the conductivity type of the semiconductor is reversed is also conceivable.

"Effects of the Invention" As explained above, according to the present invention, a first optical waveguide layer is provided on a semiconductor substrate on which a diffraction grating is formed, a depression layer having a refractive index smaller than that of the first optical waveguide layer,
Active waveguide layers having a higher refractive index than the first optical waveguide layer are sequentially laminated, and after removing a portion of the depleted layer and the active waveguide layer, the active waveguide layer is coated on the entire upper surface of the wafer. By sequentially laminating a second optical waveguide layer having the same composition as the optical waveguide layer and a cladding layer having the same refractive index as the semiconductor substrate (1), the following effect can be achieved.

(2) The unevenness of the diffraction grating does not disappear during the crystal growth process, and as a result, a high coupling coefficient (reflectance) can be obtained and a large optical output can be obtained.

■The number of times of epitaxial growth can be reduced, resulting in less thermal history applied to the wafer and improved reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention, and FIG.
The figure is a cross-sectional view showing an example of the configuration of a conventional semiconductor laser. IO... Semiconductor substrate, 11... Diffraction grating, 12... First optical waveguide layer, 13...
・Depression layer, 14...Active waveguide layer,! 5... Second optical waveguide layer, 16...
cladding layer.

Claims (1)

[Claims] A first optical waveguide layer, a depression layer having a lower refractive index than the first optical waveguide layer, and an active waveguide layer having a higher refractive index than the first optical waveguide layer are sequentially laminated on a semiconductor substrate on which a diffraction grating is formed on the upper surface. After removing a portion of the depression layer and the active waveguide layer, a second optical waveguide layer having the same composition as the first optical waveguide layer and a cladding layer having the same refractive index as the semiconductor substrate are formed on the entire upper surface of the wafer. An optical semiconductor device formed by sequentially laminating layers.