JPH04149407A - Active type wavelength selective semiconductor element - Google Patents

Abstract

PURPOSE:To restrain light emission and to improve sensitivity characteristic by forming an optical waveguide, that is, optical waveguide area of an indirect transition type semiconductor. CONSTITUTION:The element is formed of the indirect transition type optical waveguide area 3, a p-type clad area (p-type conductive area) 5 surrounding the area 3, a Bragg diffraction grating 6 for selecting wave length which is provided between the area 3 and the area 5, and a p-n junction for injecting a current in the area 3. Namely, silicon (Si) being the indirect transition type semiconductor is used as the semiconductor substrate 1. An n-type Si buffer layer (clad layer) 2 and an n-type Si/Si1-x Gex superlattice layer 3 which becomes the optical waveguide layer are successively laminated on the n-type Si substrate 1 in a molecular beam epitaxial method. In such a case, the area 3 is formed of the indirect transition type semiconductor. Then, the refractive index of the area 3 is made higher than that in the surrounding clad layer 2. Thus, the high sensitivity characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active wavelength selective semiconductor device useful for wavelength multiplexing optical communication and optical switching.

BACKGROUND OF THE INVENTION As the capacity of optical communications increases, wavelength multiplexing and division systems are attracting attention. In this method, several nanometers (nm)
Since multiplexing is performed at a wavelength interval of , a wavelength selection element with excellent wavelength resolution and a tuning mechanism is required.

Further, in optical exchange systems, a wavelength selection element is similarly desired as an interface for wavelength exchange.

A wavelength selection element with excellent wavelength resolution and a tuning mechanism has been described, for example, by Numai et al. in Applied Physics, Letters.
ters) Vol. 53 (1988) p. 83-85, λ14 for phase matching in the direction of light propagation.
Generally, a structure is adopted in which a Bragg diffraction grating including a shift region (λ is a wavelength) is provided and the refractive index of an optical waveguide (light guide region) is varied by current injection from a pn junction. The λ/4 shift structure is employed to obtain higher wavelength resolution (<lnm) compared to normal uniform diffraction gratings. At this time, the selected wavelength (Bragg wavelength) is 2neA
(ne is the effective refractive index of the waveguide, A is the pitch of the diffraction grating)
It is written as . Furthermore, in order to obtain a wide wavelength tuning range, it is obvious that ne needs to be changed significantly. Changes in the refractive index of semiconductors are brought about by the plasma effect caused by current (carrier) injection, the Pockels effect caused by the application of an electric field, the Franz-Kjelditzsch effect, etc., but in general, the refractive index change caused by the plasma effect is the largest (Δn/
n~1O-2), so it is adopted.

(Problem to be Solved by the Invention) According to the above principle, it becomes possible to extract any one signal from an optical signal multiplexed into 10 to 50 waves. However, in order to guide light efficiently, optical waveguides are usually surrounded by a semiconductor with a low refractive index, that is, a wide forbidden band width, which is a so-called double Peter structure, so it is easy to use current injection. It has the disadvantage that spontaneous emission light is generated. This spontaneously emitted light cannot be ignored compared to the intensity of the incoming signal light, and may even be greater than the intensity of the signal light. In such case,
When a light-receiving element is installed in the latter stage to perform optical reception, the reception sensitivity is greatly degraded.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and provide an active wavelength selective semiconductor device having high sensitivity characteristics.

(Means for Solving the Problems) The present invention provides an active wavelength selective semiconductor element, an optical waveguide region, a cladding region surrounding the optical waveguide region, and a wavelength-selective semiconductor device provided between the optical waveguide region and the cladding region. In an active wavelength selection semiconductor device comprising a diffraction grating for selection and a pn junction for injecting current into the optical waveguide region,
At least the optical waveguide region is made of an indirect transition type semiconductor. By making the refractive index of the optical waveguide region higher than that of the surrounding cladding layer, light can be guided well.

(Function) Since the optical waveguide region of the conventional active wavelength selection element is composed of a direct transition type semiconductor, the injected carrier-injected electron/hole pair recombines with the momentum vector of the energy band diagram at =0, resulting in light emission. do. However, according to the present invention, since at least the optical waveguide region is an indirect transition type semiconductor, carrier-injected electrons are distributed as ≠0, while holes are distributed as ≠0. Since recombination light emission is a phenomenon that occurs when the vector k is conserved, no light emission occurs in the case of the present invention.

(Example) FIG. 1 shows a schematic diagram of an active wavelength selective semiconductor device manufactured based on the present invention. Silicon (Si), which is an indirect transition type semiconductor, was used as the substrate 1. On an n-type Si substrate 1, an n-type Si buffer layer (cladding layer) 2 and an n-type Si/S which will become an optical waveguide layer are formed by molecular beam epitaxial method.
i1. Gex superlattice layers 3 were sequentially laminated. The optical waveguide layer has a superlattice structure to alleviate the occurrence of dislocations due to strain stress, and has a Si barrier of 100 layers and a 5i1-xGel-x well of 1.
00A (X=0.2) were alternately stacked for 50 cycles. Thereafter, a Bragg diffraction grating 6 including a λ/4 shift region 7 was formed using an interference exposure technique. Here, the pitch of the diffraction grating was 220 nm. After forming the diffraction grating, it was etched into mesa-shaped stripes (width 3 μm) parallel to the direction of propagation of light. The mesa height was approximately 2□m. Thereafter, the n-type cladding layer 4 was laminated again using the molecular beam epitaxial method, and the optical waveguide 3 was buried therein. The refractive index of the leading waveguide 3 is higher than that of the surrounding Si, and the structure allows light to be guided well.

A p-type conductive region (p-type cladding region) 5 was formed by selectively diffusing boron (B) from the surface of the epitaxial structure produced as described above to just above the optical waveguide. This formed a pn junction for current injection. FIG. 2 shows a cross section of the optical waveguide section viewed from a direction perpendicular to the direction in which light travels. The p-side electrode 9 and the n-side electrode 10 were each made of AuZn and AuGe alloys formed by ordinary resistance heating vapor deposition. The surface protective film 8 and the antireflection film 11 formed on the light incident surface and the light exit surface are both silicon nitride films formed by plasma CVD.

Although the explanation has been limited, it goes without saying that the same applies to the case where the p-type and n-type are reversed. Furthermore, the present invention can be similarly applied to other indirect transition type semiconductor material systems such as AlGaSb. Further, the leading wave layer may be a bulk layer limited to a superlattice.

(Effects of the Invention) A wavelength selection element having a structure similar to that shown in FIG. 1 was manufactured using a conventional direct transition type semiconductor InP/InGaAsP system, and compared with the present invention. Tunable semiconductor laser (wavelength 1.
55 μm band) was used as a transmission light source, the fiber-transmitted light was transmitted through a wavelength selection element and received by an InGaAs avalanche photodiode. Figure 3 shows the receiving sensitivity characteristics of light directly modulated at 2.5 Gb/s. The present invention improved reception sensitivity by approximately 3 dB, demonstrating the superiority of the present invention.

By configuring the optical waveguide with an indirect transition type semiconductor in this way, light emission therein can be suppressed, so that a good wavelength selection element can be obtained. When the wavelength selection element of the present invention is used in a light receiving device for optical communication, it is possible to achieve an improvement in reception sensitivity of I'J of 3 dB or more compared to the conventional device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an active wavelength selective semiconductor device showing an embodiment of the present invention, FIG. 2 is a diagram explaining the structure of the optical waveguide portion of FIG. 1, and FIG. 3 is a diagram of the device of the present invention. FIG. 3 is a receiving sensitivity characteristic diagram. In the figure, 109. Semiconductor substrate, 2-buffer layer, 3-optical waveguide region, 4-n-type cladding region,
5... p-type cladding region, 6... Bragg diffraction grating, 7... λ/4 shift region, 8... surface protective film, 9
0. . p-side electrode, 10...n-side electrode, 11... antireflection film.

Claims (1)

[Claims] an optical waveguide region, a cladding region surrounding the optical waveguide region, a diffraction grating for wavelength selection provided between the waveguide region and the cladding region, and a pn for injecting current into the waveguide region. 1. An active selective semiconductor device comprising a junction, wherein at least the optical waveguide region is comprised of an indirect transition type semiconductor.