JPH0233982A - Wavelength multiple discrimination semiconductor photodetector - Google Patents

Abstract

PURPOSE:To discriminate, absorb lights having different wavelengths, and to output as an optical current signal by forming superlattice structures having different well layer thicknesses of a waveguide structure by utilizing a growing speed in a groove with groove depth dependency. CONSTITUTION:Groove regions having 10mum of width, 3mum and 6mum of depths are formed by etching on an N-type InP substrate 1, and an N-type InP layer 2, a superlattice structure 3 made of N-type InGaAs layer/N-type InP layer, and an N-type InP layer 4 are selectively formed in the groove by a hydride UPE method. A p-type region 10 is selectively formed on the layer 4 by Zn diffusion, and a waveguide region structure is obtained in the superlattice structure under the region 10. P-type contact electrodes 5, 6 and an N-type contact electrode are provided, and an electric field is applied to the waveguides made of superlattice structure. Thus, lights having different wavelengths are discriminated, absorbed and output as an optical current signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor light-receiving device, and more particularly to a wavelength multiplexing discrimination type semiconductor light-receiving device that can discriminate and receive a plurality of lights of different wavelengths.

[Conventional technology]

Conventionally, optical communication has used a transmission method based on modulation of a single light beam. However, a wavelength multiplexing method that uses a plurality of lights of different wavelengths is attracting attention as a transmission method with higher density and higher speed. In this case, not only the light-emitting element but also the light-receiving element needs to have a function of discriminating wavelengths and identifying each signal.

Currently well-known optical communication semiconductor light-receiving devices include, for example, I
nQ, 53 Ga□, P with 47A5 layer as light absorption layer
There are IN-type light-receiving light-receiving elements, balanche multiplication type light-receiving elements, and the like. The avalanche multiplication type light receiving element has attracted attention because of its capacity and ease of processing, and because it has an internal gain effect and high speed response.

However, in these light-receiving elements, since light is normally incident perpendicularly to the layered structure, it is impossible to discriminate photocurrent signals in units of wavelengths. On the other hand, A, Larssc
n etc. are waveguide structures and absorption layers have superlattice structures.
, Pbys, Lett.

1986.49. pp233-pp235) and confirmed the functionality of wavelength discrimination. A, Lar in Figure 3
ss.

A structural diagram of a wavelength-discriminating light-receiving element such as n is shown. The layer structure includes an n-type AeGaAs layer 32 on an n-type GaAs substrate 31.
, a superlattice structure 33 consisting of an n-type aAs layer/n-type Aj'GaAS layer, and a P-type AJ7GaAs7@34. Here, by proton injection, the region 38.39
A waveguide structure is obtained by selectively forming only the P wall region.

Here, P-type contact electrodes 35, 36. By providing the n-type contact electrode 3737, each waveguide 38
Different voltages can be applied at 39°. Therefore, different absorption edge wavelengths are obtained in each waveguide due to the Stark effect in the superlattice structure. Therefore, when light having two wavelengths is incident and guided from the end face direction, the light is discriminated and absorbed by each waveguide and is obtained as a current signal by the electrodes 35 and 36, respectively.

[Problem to be solved by the invention]

In the structure described above (FIG. 3), the wavelength range in which wavelength discrimination is possible depends in principle only on the Stark effect. The Stark effect is a phenomenon in which the quantum level shifts due to deformation of the band structure when a reverse electric field is applied, and the effective electron-hole transition energy decreases.As a result, the absorption edge shifts to the long wavelength side when a reverse electric field is applied. It will be extended.

However, the application range of wavelength discrimination using the Stark effect alone is theoretically expected to be extremely narrow, and in fact, A, La
In the experiments of Rsson et al., a wavelength difference of at most 300 degrees of acidity was discriminated. Communication systems require light-receiving elements that discriminate wavelengths over a wider range of wavelengths, making them applicable to future large-capacity optical communications using wavelength multiplexing.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a wavelength multiplexing discrimination type semiconductor light-receiving element that can discriminate and receive light having a plurality of different wavelengths.

[Means to solve the problem]

The wavelength multiplexing discrimination type semiconductor light-receiving device of the present invention has a superlattice structure including a first semiconductor layer, a semiconductor layer group which is a light absorption layer and an optical waveguide layer, and a second semiconductor layer in a groove formed on a semiconductor substrate. A waveguide is formed by stacking semiconductor layers, and the semiconductor layer group is a first. The refractive index is higher than that of the second semiconductor layer, the absorption edge energy is lower, and the depths of the grooves are different in the waveguide direction.

[Effect]

The present invention has solved the problems of the prior art by taking the above-mentioned measures.

In the -m superlattice structure, the absorption edge wavelength will be different from that of normal bulk materials. In other words, the absorption edge energy becomes larger than the absorption edge of the bulk material due to the quantum leveling of holes and electrons due to the superlattice structure. This is shown in equation (1).

Here, 2 is the well layer thickness, El is the bulk energy gap, mn is the effective mass of electrons, and mp is the effective mass of holes. Here, if it is possible to partially change the well layer thickness within the same waveguide, as shown in equation (1), it is possible to achieve a much wider wavelength band than when using the conventional Stark effect. Wavelength discrimination becomes possible.

The present invention focuses on the fact that when a superlattice structure is formed in a groove, the growth rate changes depending on the groove depth. Generally, the growth rate tends to increase as the groove depth increases. Based on this experimental fact, when a layered structure with a superlattice structure is grown, the superlattice nr has a different well layer thickness depending on the groove depth.
J-construction is realized.

FIGS. 2A, 2B, and 2C illustrate the above contents. By forming grooves 22 with partially different groove depths on the substrate 21 and growing the superlattice structure 23 in these grooves,
As shown in FIGS. 2(B) and 2(C), a waveguide structure having a well layer thickness corresponding to the groove depth is obtained. Here, the absorption edge wavelength of each waveguide region 24.degree. 25 is determined according to equation (1), and the deeper the groove depth, the longer the wavelength of the absorption edge.

When light including two wavelengths is incident and guided from the end face into such a layered structure, it is discriminated and absorbed in each waveguide region, and is obtained as a photocurrent signal.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a structural diagram of a wavelength multiplexing discrimination type semiconductor light receiving element formed according to an embodiment of the present invention. This is an example of an element that discriminates between two wavelengths, and the material used is InP/InGaAs for the long wavelength optical communication band (1 to 1.6 μm band).
Needless to say, this method can also be applied to material systems such as aAs/GaAs.

Here, a groove width of 10 μm is formed on the n-type InP substrate 1.

A groove region having a depth of 3 μm and 6 μm is formed by etching, and then an n-type InP layer 2. n-type I nGaAs layer/n-type I
Superlattice structure made of nPM3. An n-type InPJt 14 is formed. Here, a P-type head region 10 is selectively formed in the n-type InP layer 4 by Zn diffusion, and a waveguide region structure is obtained in the superlattice structure under this P-type region. Further, by providing electrodes 5 and 6 for P-type contacts and electrodes for N-type contacts 1 to 1, an electric field is applied to each waveguide having a superlattice structure.
Moreover, the photocurrent signal can be extracted. Note that the effective refractive index of the superlattice structure 3 is larger than that of the InP layer,
Moreover, since the absorption edge energy is small, the conditions for an optical waveguide are satisfied.

In this case, the growth rate in a trench with a trench depth of 6 μm is 3 μm deep.
It has been experimentally found that the depth is approximately 1.5 times larger than the depth 6.m. The well layer thickness at um thickness is 7
There were 5 people, and the thickness of the well layer in the 3 μm deep groove was about 50 people. Therefore, the limit on the long wavelength side of the absorption edge wavelength estimated from equation (1) is 1.38 μm in a waveguide region with a groove depth of 6 μm.
The groove depth is 1.11 μm in the waveguide head area of 3 μm. For example, this is light containing two wavelengths of 1.11 μm and 1.38 μm]
By inputting and guiding the 1.11 μm light from the waveguide area side of the shallow groove to the end face, the 1.11 μm light is transmitted to the waveguide area of the shallow groove side.
．． It becomes possible to discriminate and absorb 38 μm light in the waveguide region on the deep groove side and extract it from the electrode 5.6 as a photocurrent signal.

In this case, the wavelength range in which wavelength discrimination is possible extends to 2,700 people, and it is possible to discriminate a wider range of wavelengths than a conventional element that uses only the Stark effect.

In this embodiment, the case of discriminating light with two wavelengths has been described, but in order to discriminate light with N wavelengths, a layered structure is formed in a groove consisting of N regions with different groove depths according to the present manufacturing method. It becomes possible.

〔Effect of the invention〕

As explained above, the wavelength multiplexing discrimination type semiconductor light-receiving device obtained according to the present invention utilizes the fact that the growth rate in the trench is dependent on the trench depth to create a superlattice structure with different well layer thicknesses. By creating a wave path structure, it becomes possible to discriminate and absorb light of different wavelengths and extract it as a photocurrent signal. This makes it possible to easily discriminate wavelengths and receive light on one chip in wavelength multiplexed optical communication.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a wavelength multiplexing discrimination type semiconductor light-receiving element that can discriminate between two wavelengths of light, which is an embodiment of the present invention, and FIGS. 2(A) and 2(B). (C) is a diagram illustrating a manufacturing method of growing a superlattice structure in grooves of different groove depths, which is a feature of the present invention, and FIG. 3 is a diagram of a wavelength multiplexing discrimination type semiconductor light-receiving device according to the prior art. 1---- n-type InP substrate, 2-n-type TnPl, 3...
・N-type InGaAs layer/n-type InP layer superlattice structure, 4・
...n-type InP layer, 5...P-type electrode, 6...P-type electrode, 7...n-type electrode, 10...Zn diffusion region (P-type head region), 12:2 wavelength Incident light including, 2]...Semiconductor substrate, 22...Groove, 23...Semiconductor superlattice structure, 2
4... Waveguide region, 25... Waveguide region, 31...n
Type GaAs substrate, 32-n type AJ? GaAs layer, 33.
N-type GaAs layer/n-type Al2GaAs layer superlattice structure 5, 34-P-type AffGaAs layer, 5... Electrode for P-type contact, 6... Electrode for P-type contact, 37... For n-type contact Electrode, 38... Waveguide region, 9... Waveguide region.

Claims (1)

[Claims] A first semiconductor layer, a superlattice structure consisting of a group of semiconductor layers in which two types of semiconductor layers with different forbidden band widths are alternately stacked, and a second semiconductor layer are stacked in a trench formed on a semiconductor substrate. The semiconductor layer group constitutes a waveguide, and the semiconductor layer group includes the first and second semiconductor layers.
1. A wavelength multiplexing discrimination type semiconductor light-receiving element having a higher refractive index and lower absorption edge energy than the semiconductor layer of the present invention, and wherein the depth of the groove is different in the waveguide direction.