Voltage tunable schottky diode photoemissive infrared detector

Abstract

PtSi/Si Schottky diode infrared detectors are currently being used in large-area focal plane arrays for imaging in the 3-5 micron atmospheric transmission window. Their photoresponse cuts off at about 6 microns, beyond which they cannot detect infrared ratiation. Because of the nature of Schottky diodes, this cut-off wavelength cannot be adjusted during operation, but is relatively fixed, varying only in proportion of the fourth root of an externally applied bias. This disclosure describes a Schottky diode infrared detector with a voltage-tunable cut-off wavelength. The tunability is obtained by modification of the Schottky diode band diagram by insertion of a SiGe layer, with the appropriate parameters, between the silicide and the Si substrate, making the detector a silicide/SiGe/Si Schottky diode detector. The SiGe/Si interface has a valence band offset that can be used to engineer the shape, or depth profile, of the Schottky barrier. The energy offset can be gradual or abrupt, depending on the grading of the Ge concentration in the SiGe layer. When the offset is abrupt, it can be thought of as an additional, higher energy barrier to photoemitted carriers if the SiGe layer is thin enough. Because this offset, gradual or abrupt, is designed to be deeper in the semiconductor than the normal Schottky barrier maximum, it is easily modified by an external applied voltage. The sensitivity and the range of tunability are defined by the SiGe thickness and Ge concentration, respectively.