Browse Prior Art Database

Photo-Gate Fet

IP.com Disclosure Number: IPCOM000035082D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Chappell, TI: AUTHOR [+2]

Abstract

A photovoltaic detector is integrated into the gate of a GaAs MESFET. In order to get the needed depletion beneath the gate, surface states are intentionally created during the growth step for the photo-gate such as by molecular beam epitaxy (MBE) by allowing some oxygen into the MBE system just prior to the growth of the multilayer photo-gate. The structure and the location of these surface states is shown in Fig. l.

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Photo-Gate Fet

A photovoltaic detector is integrated into the gate of a GaAs MESFET. In order to get the needed depletion beneath the gate, surface states are intentionally created during the growth step for the photo-gate such as by molecular beam epitaxy (MBE) by allowing some oxygen into the MBE system just prior to the growth of the multilayer photo-gate. The structure and the location of these surface states is shown in Fig. l.

In operation, light falls on the photo-gate, generates hole- electron pairs which produce several volts under open-circuit conditions, and this forward biases the Schottky gate of the MESFET, turning it on. The forward biasing of the Schottky limits the actual voltage swing on the gate to less than one volt, providing a low impedance load for the photo-gate structure which leads to a fast transient response in the photo-gate. The device can be wired as a source follower to provide a low impedance output for driving the following stages, either on-chip for signal processing, such as clock extraction, serial to parallel conversion, decoding and buffering, or off-chip, such as a separate signal processing chip, as in Fig. 2. Because the parasitic capacitance is held to the absolute minimum in the device and essentially no minority carrier charge storage whose removal is diffusion limited, the operating speed can be very high,
i.e., in the GHz range.

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