JPS59226320A - Semiconductor diffraction grating - Google Patents

Abstract

PURPOSE:To make diffraction efficiency changeable by a reverse bias voltage by forming (+) conduction type semiconductor layers divided at a specified interval on a semiconductor layer of a (-) conduction type and providing an electrode layer and a voltage impressing device so that the p-n junction interface is reverse biased. CONSTITUTION:A p-InP: Zn (10<16>cm<-3> impurity concn.) crystal or the like is used as a substrate 1 and semiconductor layers 2 of n-InP: Sn (10<16>cm<-3> impurity concn.) or the like are formed thereon at every specified interval. Metallic electrode layers 3 consisting of 10% Sn/Au, etc. are formed on the layers 2 and an electrode layer 4 consisting of 10% Zn/Au is formed on the bottom surface of the substrate 1. When the p-n junction interface between the substrate 1 and the electrode layers is reverse biased by a voltage impressing device 5, a diffraction grating having the diffraction efficiency variable with the magnitude of the impressed voltage is obtd. The diffraction grating is thus made suitable as a diffraction grating particularly for a distribution feedback type semiconductor laser or the like which is a light source for stabilizing wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The semiconductor diffraction grating according to the present invention can be used in fields that utilize the inherent characteristics of light. It is useful not only in the field of optical communications but also in fields related to optical disks, which have been rapidly developing recently. In particular, it can be used as a diffraction grating for distributed feedback semiconductor lasers and Bragg reflection feedback semiconductor lasers, which are wavelength stabilized light sources and light sources for optical ICs. Furthermore, in the future, it can become a constituent element of optical logic circuits and can be used in the field of optical computers.

Structure of a conventional example and its problems A conventional semiconductor diffraction grating realizes a periodic structure of changing refractive index by periodically forming irregularities on a semiconductor surface.

These have already been applied to distributed feedback semiconductor lasers and Bragg reflection feedback semiconductor lasers. However, in this conventional semiconductor diffraction grating, the periodic structure of the refractive index change is uniquely determined by the shape of the unevenness formed on the semiconductor surface and the refractive index of the semiconductor material used. It was not possible to externally modulate the periodic changes in . That is, the diffraction efficiency of a diffraction grating is determined by its shape and the refractive index of the material used, and it has been impossible to change it from the outside.

Purpose of the Invention The present invention improves the conventional problems as described above,
In order to achieve modulation of diffraction efficiency, the present invention provides a semiconductor diffraction grating with a new structure, assuming that it will be used as a constituent element of an optical integrated circuit in the future.

Structure of the Invention A semiconductor diffraction grating according to the present invention is formed in a first semiconductor layer having a -conductivity type, and the first semiconductor layer,
a second semiconductor layer having a conductivity type different from that of the first semiconductor layer divided at regular intervals; a first electrode layer formed on the second semiconductor layer; and a bottom layer of the first semiconductor layer. a second electrode layer formed on the surface, that is, a surface on which the second semiconductor layer is not formed, the first electrode layer and the second electrode layer;
and means for applying a voltage between the electrode layer and the electrode layer.

DESCRIPTION OF EMBODIMENTS Generally, in a semiconductor diffraction grating, light propagating through the first semiconductor layer has periodic changes in the refractive index on the first semiconductor layer, that is, the refractive index of the second semiconductor layer and the second semiconductor layer. Diffraction occurs due to periodic changes in the refractive index of the portions where no semiconductor layer is formed. Further, the diffraction efficiency is proportional to the difference in refractive index between the second semiconductor layer and the portion where the second semiconductor layer is not formed. According to the semiconductor diffraction grating according to the present invention, similarly to conventional semiconductor diffraction gratings, light propagating through the first semiconductor layer depends on the embedding index of the second semiconductor layer and the formation of the second semiconductor layer. Diffraction occurs due to periodic changes in the refractive index of the non-containing parts.

However, the p of the first semiconductor layer and the second semiconductor layer
When a voltage is applied so as to apply a reverse bias to the -n junction interface, the refractive index of the second semiconductor layer increases, the periodic change in the refractive index is modulated, and as a result, the diffraction effect also increases. This is because when a reverse bias is applied, the depletion layer expands, the carrier concentration in the second semiconductor layer decreases, and the refractive index increases, resulting in refraction with the part where the second semiconductor layer is not formed. As the index difference increases, the diffraction efficiency also increases. ' As described above, according to the present invention, it is possible to change the diffraction efficiency depending on the magnitude of the voltage applied from the outside.

Example 1 FIG. 1 shows a cross-sectional view of a configuration example in which InP is used in a semiconductor diffraction grating according to the present invention. That is, as the substrate crystal 1, P-InP: Zn (impurity concentration 10
cm ) crystals are used, and a certain interval (0.4 μm) is placed on top of the crystal.
), the semiconductor layer 2 with a width of 0.4 μm and a thickness of 0.4 μm is formed with n-1nP;Sn (impurity concentration 10
cm) is used. Further, an electrode layer 3 made of metal formed on the semiconductor layer 2 is made of 10% Sn/Au, and an electrode layer 4 made of metal formed on the lower surface of the substrate crystal 1 is used.
10% Zn/Au is used. Furthermore, a device 5 for applying a voltage between the electrode layer 3 and the electrode layer 4 is provided.

2 is light.

This semiconductor grating according to the invention exhibits only the same behavior as a conventional semiconductor grating when no external voltage is applied. However, the electrode layer 3 and the electrode layer 4 are arranged so that a reverse bias is applied to the p-n junction interface between the substrate crystal 1 and the semiconductor layer 2.
When a voltage is applied between them, it functions as a diffraction grating with variable diffraction efficiency. That is, when a reverse bias is applied, the depletion layer existing at the p-n junction interface between the semiconductor layer 1 and the semiconductor layer 2 expands, and as a result, the Yayaria concentration decreases and the refractive index increases. If the applied reverse bias is increased, the depletion layer also becomes larger, so it is possible to change the increased portion of the refractive index depending on the magnitude of the reverse bias. As a result, the diffraction efficiency becomes variable. In this example, InP is used as the material, but InGaAsP is used as the material.
The same effect can be achieved by using a mixed crystal such as . ' Example 2 Next, in the semiconductor diffraction grating according to the present invention, the substrate crystal 1
FIG. 2 shows a specific example of a mixed structure including an optical waveguide layer 6 for light a between the semiconductor layer 20 and the semiconductor layer 20. In this case, the semiconductor layer serving as the optical waveguide layer is made of p-InGaAsP quaternary mixed crystal. The other components are the same as those used in Example 1. In this case, the voltage application method and the function of the entire diffraction grating are the same as in the first embodiment.

Example 3 Next, in the semiconductor diffraction grating according to the present invention, the spaces between the semiconductor layers 2 divided at regular intervals are filled with a semi-insulating semiconductor layer or a semiconductor layer 7 having a conductivity type different from that of the semiconductor layer 2. A specific example of the configuration is shown in FIG. In this case, the semiconductor layer 7 is ion-implanted with InP.
layer or p-InP; Zn (impurity concentration 1016
an-5), and the other materials were the same as those used in Example 1. Further, the voltage application method and the function of the entire diffraction grating in this case are also the same as in the first embodiment.

Furthermore, in the embodiments described above, InP-InGaA
Although it was explained in terms of sP-based semiconductors, GaAs-GaAR
Not only can it be realized in the same way with other ■-V group semiconductors such as As-based semiconductors, but also with n-Vl group compound semiconductors such as Zn5e.
It is also possible to realize this by using group semiconductors at the same time.

As described in detail, the semiconductor diffraction grating according to the present invention has a semiconductor layer constituting the convex portion of the semiconductor grating and a semiconductor layer below the semiconductor layer having different conductivity types, and a reverse bias is applied to the p-n junction interface. The electrode layer and the voltage application device (+iii) are arranged so that the voltage can be applied, and the diffraction efficiency can be changed depending on the magnitude of the reverse bias voltage. When used as a diffraction grating for a Bragg semi-pair type semiconductor laser, it is possible to modulate the amount of feedback of the laser light, and therefore it is possible to modulate the light emitted from the semiconductor laser.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor diffraction grating according to an embodiment of the present invention;
Figure 2 is a cross-sectional view of a semiconductor diffraction grating equipped with an optical waveguide layer;
FIG. 3 is a cross-sectional view of a semiconductor diffraction grating in which the spaces between the semiconductor layers are filled with a semi-insulating semiconductor layer or a semiconductor layer having a conductivity type different from that of the semiconductor layer. 1... p-InP substrate, 2... n-I
nP substrate layer, 3.4... Electrode layer, 5...
・Voltage application device, 6...p-InGaAsP
Optical waveguide layer, 7...B Ion-implanted InP layer or p-InP layer. Name of agent: Patent attorney Toshio Nakao and 1 other person-1
(

Claims (2)

[Claims] (1) - A first semiconductor layer having a conductivity type, and a first semiconductor layer formed on the first semiconductor layer and divided at regular intervals.
a second semiconductor layer having a conductivity type different from that of the semiconductor layer;
a first electrode layer formed on the second semiconductor layer; a second electrode layer formed on the surface of the first semiconductor layer on which the second semiconductor layer is not formed; A semiconductor diffraction grating comprising a voltage applying means for applying a voltage between the first electrode layer and the second electrode layer. (2) A claim characterized in that a semi-insulating semiconductor layer or a semiconductor layer having a conductivity type different from that of the second semiconductor layer is provided between the second semiconductor layers divided at regular intervals. The semiconductor diffraction grating according to item 1.