JPS61283178A - Photoconductive type semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain a high speed response by forming a P-N junction in a semiconductor layer having large similar forbidden band width, and depleting by the application of reverse bias over a photoabsorbing layer having small forbidden band width. CONSTITUTION:An N-type AlInAs layers 2 of approx. 0.5mum, an N<-> type AlInAs layer 3 of 0.3mum are formed by epitaxially growing method on an N<-> type InP substrate 1, and an N<-> type InGaAs layer 4 of approx. 2mum and an N<-> type InP layer 5 of approx. 1.5mum thick are formed. With an SiO2 film as a selectively diffused mask on the wafer thus obtained, and Zn is diffused to form a P<+> type InP region 6. After an AuGe alloy is, for example, deposited, the region except the prescribed region is removed, and heat treated at high temperature. Thus, an N<+> type region 7 is formed, lead removing electrodes 8, 8' are then formed to form a photoconductive type photodetector.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photoconductive semiconductor light-receiving element as a photodetector used in optical communication, optical information processing, etc.

[Conventional technology]

Semiconductor photodetectors are important as photodetectors in optical communication systems for long-distance, large-capacity or optical information processing, and their research and development are progressing along with semiconductor lasers or light-emitting diodes as light sources. Photoconductive semiconductor light-receiving devices using compound semiconductors have attracted attention because they can be obtained by a relatively simple method and have the potential for high speed and high sensitivity9. Avalanche photodiodes, or even photodiodes, are expected to have excellent characteristics.

Conventionally, in order to obtain high-speed response, there has been a report on the structure shown in Figure 3 as a photoconductive type semiconductor light-receiving element that utilizes two-dimensional electron gas [Applied Physics Letters (Ap.
pl-Phys, Lett,, 43[3)e I
August 1983)]. In this example, n-I
nGaAs13 f light absorption layer, in the valley region in the low concentration InGaAs13 layer caused by conductor discontinuity due to the junction of InGaAs13 and n-AtInAs12,14,
By spatially confining the inner cage of photoexcited carriers, the high mobility of electrons without scattering by donor ions etc. is utilized. The device thus obtained has a rise time of 80p! 11! +(+, reported to exhibit a photoresponse characteristic with a full width at half maximum of 250 psec, but a slow photoresponse on the order of n sec determined by the slow drift velocity of holes was observed as a long tail.

In the figure, 11 is a semi-insulating InP substrate, 15 is an n”-Galn
As, 16 is an electrode.

A photoconductive semiconductor light-receiving element with a structure as shown in Fig. 4 has also been reported for the purpose of eliminating such deterioration in the fall of the pulse response, that is, the influence of slow holes [Applied Physics Letters]. , Phys.

Lett0m43QJ-15Deasmber 198
3) "l. In this example, GaAs 23 is used as a light absorption layer, and two-dimensional electron gas generated in n-GaA+s 24 by joining n-GaAs 24 and n-AtGaAa 25 is used. P-GaAs substrate 21 is used as a light absorption layer. By applying a reverse bias, the holes are taken out from the holes (t-ff-) and do not contribute to the photocurrent flowing between the source and drain, resulting in an 80 p sea without slow components.
It has been reported that a certain amount of time has been obtained for the downtime.

In the figure, 22 is p-GaAs, 26 is n-GaAm
.

27 is an f-) electrode, and 28 is an electrode.

[Problem that the invention seeks to solve]

However, the extraction of slow components by such darts results in a decrease in optical-to-electrical signal conversion efficiency, and is not necessarily suitable as a photodetector for optical communication systems that require a high signal/noise ratio. do not have.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photoconductive semiconductor light-receiving device which eliminates such conventional drawbacks, maintains high optical-to-electrical signal conversion efficiency, and has high-speed response characteristics.

[Means for solving problems]

The present invention provides a semiconductor having at least semiconductor layers of the same conductivity type with different forbidden band widths in contact with each other, in which a region of the semiconductor layer with the large forbidden band width that is not in contact with the semiconductor layer with the small forbidden band width is of the conductive type. A p-n junction is formed by forming a semiconductor region of the opposite conductivity type, and by applying a reverse bias to this p-n junction, it is possible to prevent depletion of the semiconductor layer with a small forbidden band width. Features.

[Action/Principle]

By forming a p-n junction in a semiconductor layer with a large forbidden band width, applying a reverse bias to this p-n junction, and depleting the light absorption layer with a small forbidden band width), In this book, among electron and hole pairs generated by photoexcitation in a semiconductor layer with a small forbidden band width, carriers that become minority carriers are generated by band discontinuity caused by the band structure of two semiconductors with different forbidden band widths. By performing two-dimensional gasification, it was possible to obtain a high-speed response.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one embodiment of the present invention. In this example, first, n+-InP having (100) plane
An n-AtInAa layer 2 with a film thickness of 0.51Rn and an impurity concentration I x 1017z-' is grown on the substrate 1 by an epitaxial growth method (side-light molecular beam epitaxial growth method). -AAI
After forming the nAs layer 3, the film thickness is 2 μm and the impurity concentration is 5×10
An n-InGaAs layer 4 with a thickness of 1.5 μm and an n-InP layer 5 with an impurity concentration of 5×10”m are formed on the wafer thus obtained. For example, a 5IO2 film is used as a selective diffusion mask on the wafer thus obtained. The p-InP region 6 is formed by selectively diffusing, for example, Zn.

Next, after depositing, for example, an AuGe alloy, the area outside the predetermined area is removed, and then high temperature treatment is performed to form the n-region 7. After that, lead wire extraction electrodes 8 and 8' are formed to conduct photoconductivity. Complete the type photodetector.

The effects of the embodiment of the present invention described above will be explained using the schematic band structure diagram shown in FIG. The optical signal is transmitted through the light absorption layer In
Electron-hole pairs that are absorbed and photoexcited in the GaAs layer 4 are generated. Among these, the electrons are connected to the A/JnAa layer 3 and the InG
Due to the band distortion in the InGaAs layer 4 caused by the discontinuity of the conductor in the aAs layer 4, the holes move to the two-dimensional gas region, while the holes are formed in the InP layers 5 and 6. By applying a reverse bias to the p-n junction, the depletion layer spreads into the n-InGaAs layer 4, and the holes due to
Move to the dimensional gas formation area.

At this time, in FIG. 1, a potential difference is applied between the electrodes 8 and 8 to form a source and drain, and the two-dimensional gas of holes and electrons can be extracted at high speed.

〔Effect of the invention〕

As explained in detail above, according to the present invention, it is possible to two-dimensionally gasify both photoexcited carriers), suppress a decrease in photo-electrical signal conversion efficiency, and have high-speed response characteristics. This has the effect of providing a light receiving element.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of one embodiment of the present invention, FIG. 2 is a schematic diagram of the band structure for explaining the effect of the device with the structure of FIG. 1, and FIGS. 3 and 4 are the conventional FIG. 2 is a schematic cross-sectional view of a photoconductive semiconductor light-receiving element. 1 ・= n-InP substrate, 2- n-AtInAa
, :l...n-gInAs, 4...n-InGaA
s, 5-n-InP, 6-·p-InP. 7...n region, 8...electrode. 4, -TL-ITLG(LAS 5...-n-rThP Figure 2 10th stroke Z Old 2 1111-1

Claims (1)

[Claims] (1) In a semiconductor having at least semiconductor layers of the same conductivity type with different forbidden band widths in contact with each other, a region of the semiconductor layer with a large forbidden band width that is not in contact with the semiconductor layer with a small forbidden band width has a conductivity type of the above conductivity type. A p-n junction is formed by forming a semiconductor region of the opposite conductivity type, and by applying a reverse bias to this p-n junction, the semiconductor layer having a small forbidden band width is depleted. Features of photoconductive semiconductor light-receiving device.