Sensitization pretreatment of Pb-salt epitaxial films for Schottky diodes by sulfur vapor exposure

Abstract

In a process for preparing an infrared sentitive photodiode comprising the teps of: (1) forming by vacuum deposition an epitaxial layer of a semiconductor alloy material selected from the group consissting of PbSe, PbTe, PbSe.sub.x Te.sub.1-x, Pb.sub.y Sn.sub.1-y Se, Pb.sub.y Sn.sub.1-y Te, Pb.sub.y Sn.sub.1-y Se.sub.x Te.sub.1-x, Pb.sub.z Cd.sub.1-z Se, Pb.sub.z Cd.sub.1-z Te, and Pb.sub.z Cd.sub.1-x Se.sub.x Te.sub.1-x, wherein 0<x<1, 0<y<1, and 0<z-1, to cover at least a portion of the surface of a substrate composed of an infrared transparent single crystal material selected from the group consisting of (a) alkali metal halides and (b) alkaline earth halides; (2) coating the epitaxial layer of semiconductor alloy material with a thin layer of a lead halide selected from the group consisting of PbCl.sub.2, PbBr.sub.2, PbF.sub.2, and mixtures thereof by exposing the epitaxial layer alloy material to vapor of the lead halide in the presence of a gas selected from the group consisting of air, oxygen, and oxygen/inert gas mixtures; (3) vacuum depositing Pb metal onto a portion of a lead halide coated epitaxial layer of semiconductor alloy material to form a non-Ohmic Pb metal contact; and (4) forming an Ohmic contact on another portion of the epitaxial layer of semiconductor alloy material; The improvement comprising: after step (1) but before step (2), vacuum depositing a thin coating of sulfur onto the epitaxial layer of semiconductor alloy material by exposing the epitaxial layer to sulfur vapor wherein (a) sulfur vapor is maintained at a temperature T.sub.1 wherein 96.degree. C..ltoreq.T.sub.1 .ltoreq.106.degree. C., (b) the epitaxial layer of semiconductor alloy material is maintained at a temperature T.sub.2 wherein 86.degree. C..ltoreq.T.sub.2 <96.degree. C., (c) 0.degree. C..ltoreq.T.sub.1 -T.sub.2 .ltoreq.10.degree. C. and (d) the pressure is kept at no more than 10.sup.-2 torr during the sulfur vapor deposition and subsequent cool down to room temperature.

Dependencies are inferred from the claim text.