A SILICON HOMOJUNCTION INFRARED DETECTOR HAVING AN ACTIVE METAL-FILM ON AN N++ LAYER

A silicon n++pn homojunction infrared detector, in which a degenerate n++ layer is backed by a metal film forming an ohmic contact, has been proposed and studied. The metal film is a photoelectric conversion re gion along with the n++ layer. Although, for an n++pn detector without the metal film, very poor rectifying properties are observed when the n++ layer thickness is extremely reduced, the new detector, employing a thin PtSi film as the metal film, shows normal diode I-V characteri stics, since the PtSi film provides increased surface conductivity. Th e new detector has achieved an increase in operatable temperature, or an extension of cutoff wavelength, and operated with cutoff wavelength s of 11.9 mum, 18.7 mum and about 30 mum at 70 K, 50 K, and 30 K, resp ectively, because the saturation current density for the new detector has been reduced to about one tenth that for the previously reported n ++pn detector. The responsivity for the new detector has increased to 1.1-3.8 times as large as that for the previously reported n++pn detec tor, when both detectors have the same cutoff wavelength.