JPS6255969A - Photoconductive semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain a photodetector having high speed responsiveness by forming a P-N junction in a semiconductor layer having a large forbidden band width, and depleting a light absorbing layer having a small forbidden band width by means of an inner electric field to secondarily gasify a light-excited carrier. CONSTITUTION:An n-type A InAs layer 2 of 1X10<17> of impurity density, an n<-> type A InAs layer 3 of 1X10<15> of impurity density, an n<-> type InGaAs layer 4 of 1X10<14> of impurity density, an n<-> type InGaAs layer 5 of 5X10<14> of impurity density, an P<+> type InP layer 6 of 1X10<18> of impurity density are laminated and epitaxially grown on an n<+> type InP substrate 1 having (100) plane. Then, an n<+> type region 7 to become source and drain regions is formed at the opposed peripheral edges by diffusing to intrude to the layer 2, and leads leading electrodes 8 are coated on the surface. Thus, incident light signal is absorbed by the layer 4, electron-hole pairs are generated, the electrons are moved to the secondary gas region by the bent of a band in the layer 4, and the holes are moved to the secondary gas region expanded by the inner electric field generated by P<+>-N<-> junction of the layers 5 and 6.

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.

[Prior art and its problems]

Semiconductor light-receiving elements 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. As such a semiconductor light-receiving device, a photoconductive semiconductor light-receiving device using a compound semiconductor has been attracting attention because it can be obtained by a relatively simple method and has the possibility of high speed and high sensitivity. avalanche photodiode.

Alternatively, it is desired to realize characteristics as excellent as those of photodiodes.

Conventionally, as a photoconductive type semiconductor light-receiving element that utilizes two-dimensional electron gas to obtain a high-speed response, a structure shown in Figure 3 has been reported [1 bu 1', 7 + zyx, letter (^ pp1.Phys, LetL,, 43(3), 1
＾gust 191t3) ). In this example, n
”' -10G, ^, 4 is the light absorption layer, n -1
oGaAs4 and n −^f1. A.3. and n-A sentence ■, , G, A, , spatially transfers the inner molecules of photoexcited carriers to the valley region in the low-concentration n''' InGa^34 caused by the conductor discontinuity due to the junction of 2. The high mobility of electrons, which is not scattered by donor ions etc., is utilized by confining the electrons in the nanoparticles.It is reported that the device obtained in this way exhibited photoresponse characteristics with a rise time of 80 psec and a full width at half maximum of 250 psec. However, a slow photoresponse on the order of n sec determined by the slow drift velocity of the holes was observed as a long tail.

In order to eliminate such deterioration in the fall of the pulse response, that is, the influence of slow holes, a semiconducting semiconductor photodetector with a structure as shown in Figure 4 has also been reported. pp1. Phys, Lett,, 43
(12), 15December 1983)) In this example, p--G, A, 13 are light absorption layers, and n
The two-dimensional electron gas generated in n-GaAs 14 by bonding with GaAs 14 A-5 GaAs 15 is utilized.The p'' GaAs substrate 11 is used as a gate, and holes are taken out from the gate by applying a reverse bias. They report that by not contributing to the photocurrent flowing between the source and drain, a fall time of about 3 Q Psec without slow components can be obtained. However, the extraction of slow components by such gates is based on 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. Not yet.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a photoconductive semiconductor light-receiving element that eliminates these conventional drawbacks, maintains high optical-to-electrical signal conversion efficiency, and has high-speed response characteristics.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides at least a semiconductor having adjacent semiconductor layers of the same conductivity type with different forbidden band widths, in which a semiconductor layer having a large forbidden band width in the semiconductor layer has a small forbidden band width. By forming a semiconductor layer or a semiconductor region of a conductivity type opposite to the above conductivity type in a region not in contact with the semiconductor layer, depletion occurs across the two semiconductor layers of the same conductivity type and different forbidden band widths. shall be.

[Action/Principle]

The present invention solves the problems of the prior art by the above means. That is, as mentioned above, p is present in the semiconductor layer with a large forbidden band width.
, an n-junction is formed, and this internal electric field depletes the light absorption layer with a small bandgap, resulting in minority carriers among electron-hole pairs generated by photoexcitation in the semiconductor layer with a small bandgap. It has become possible to obtain a high-speed response by two-dimensionally gasifying the carriers resulting from the band discontinuity caused by the band structure of two semiconductors with different forbidden band widths.

〔Example〕

Embodiments 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”-1,P having a (100) plane
A layer 2 of n-A, flOA with a film thickness of 0.5 μm and an impurity concentration of I x 1017 cm-' is formed on the substrate 1 by an epitaxial growth method (e.g., molecular beam epitaxial growth method).
．． Film thickness 0.3μm, impurity concentration 1×1011015C1
n --Aj! -1, A, film thickness 2 μm after forming layer 3
, n--In with impurity concentration 5 x 1014C11-9
GaA, layer 4. Film thickness 0.2μm, impurity concentration 5X10”
'1 n -1, P layer 5. Film thickness 0.5μ
m, p+ of impurity f7I concentration I x 1018 cm-3
I. Two layers 6 are formed.

Next, to form the source and drain regions, for example A
After the t+Ge alloy is deposited, portions other than the predetermined regions are removed, and then high-temperature heat treatment is performed to form the n4 region 7. Then, by forming an electrode 8 for taking out a lead wire in this n1 region 7, the photoconductive type light receiving element of this embodiment is obtained.

The operation of the light receiving element according to the embodiment of the present invention described above will be explained using the schematic band structure diagram shown in FIG. The incident optical signal is absorbed by the n--1n GaAs layer 4, which is a light absorption layer, and photoexcited electron-hole pairs are generated.

Among these, the electron is n-1^11. A, layer 3 and n--1, G
.

^1n−1nGa not caused by conduction band discontinuity in layer 4
A.

The holes move to the two-dimensional gas region due to band bending within layer 4, while holes move between n--1, P layer 5 and p"-1, P layer 6.
The holes move to the two-dimensional gas formation region due to the expansion of n-1, G, ^84 of the depletion layer caused by the internal electric field due to the p+-n- junction formed by the hole. At this time, a potential difference is applied between the electrodes 8 described in FIG. 1 above to form a source and a drain, and the holes and electrons are
Dimensional gas can be extracted at high speed.

In addition, in the above embodiment, 1. Using P substrate, I, G.

Although a case has been described in which the third layer is used as a light absorption layer, the present invention is not limited to this example, and any combination of compound semiconductors satisfying the band m distribution as shown in FIG. 2 may be used.

〔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 optical-electrical signal conversion efficiency, and provide a photoconductive semiconductor light-receiving element that has high-speed response characteristics. can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of the present invention, and FIG.
FIG. 1 is a schematic diagram of a band structure for explaining the operation, and FIGS. 3 and 4 are schematic cross-sectional diagrams of a conventional photoconductive semiconductor light-receiving element. 1...n+~ll1IP board, 2-n-1'1nA
s, 3...n--^J! -1nA,,4-・n--1
,,GaAs,5-=nl. P, 6...p''-1
, P, 7...n+ region 8...electrode, 9-...
Semi-insulating 1. P substrate, 10-n”-G, IIIA,
,...ρ--G,A,, 14-n-GaA,,
15-n”-^J!Ga person 5.16-n”-GaA
a.1? - Gate electrode.

Claims (1)

[Claims] A semiconductor layer structure in which at least semiconductor layers of the same conductivity type with different forbidden band widths are bonded, and a region of the semiconductor layer with a large band gap that is not bonded to a semiconductor layer with a small band gap has a conductivity type opposite to that of the conductivity type. 1. A photoconductive semiconductor light-receiving device, characterized in that by forming a semiconductor layer or a semiconductor region of a conductivity type, depletion occurs across the two semiconductor layers of the same conductivity type and different forbidden band widths.