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Browse Prior Art Database

High Speed Heterojunction Photodetector

IP.com Disclosure Number: IPCOM000076518D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Hovel, RJ: AUTHOR [+2]

Abstract

This photodetector has fast response times (rise time approximately 10/-10/ second), can be made in a relatively large area (11 x 11 mils) without degrading the response time, and has a wide spectral response (0.7-2.7 ev).

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High Speed Heterojunction Photodetector

This photodetector has fast response times (rise time approximately 10/-10/ second), can be made in a relatively large area (11 x 11 mils) without degrading the response time, and has a wide spectral response (0.7-2.7 ev).

Presently used semiconductor photodetectors employ conventional homojunctions or heterojunctions in which a high-field depletion region is used to separate photogenerated charges in the semiconductor. Since a relatively large depletion capacitance is associated with the depletion region, there is a limitation on response speed of the photodetector. In order to minimize this capacitance, prior art photodetectors are generally made with small areas; however, it is difficult to make contact to the small areas and the contact itself obscures a large percentage of the active region of the device. Consequently, the sensitivity of the prior photodetectors is reduced and special optics are required to focus the light to a very small spot.

In the present photodetector, no depletion region or depletion capacitance is generated. The photodetector is a heterojunction structure made with semiconductors having close values of electron affinity, An example is Ge-ZnSe, which is indicated in Fig. 1. Although this photodetector has no junction capacitance, there is still a small "geometrical" capacitance which is formed by the thickness of the ZnSe in the contact area which is indicated by the capacitance C. A sheet of high-conductivity ZnSe forms the anode and is contacted with a metal ring contact 10. The cathode of the source is connected to the Ge region.

Another version of the photodetector can be made by replacing the Ge material with material which is p-type GsAs at the heterojunction interface, and which rapidly changes to p-type GaAlAs with distance from the junction. The advantage of this structure is that the photogenerated electrons find themselves in a potential which forces them toward the collector. This provides a more effective collection of electrons...