An infrared sensitive photodiode which is made of an epitaxial layer of a miconductor alloy which is a lead chalcogenide, a lead-tin chalcogenide, or a lead-cadmium chalcogenide grown on a single crystal substrate of an infrared transparent, electrically insulating material, an Ohmic contact deposited on the epitaxial layer, and a non-Ohmic Pb metal contact deposited on the epitaxial layer to form a Schottky barrier, the improvement comprising the inclusion of halide ions in the interface region between the non-Ohmic lead metal contact and the epitaxial layer of semiconductor material.
Radiation absorbing layers of epitaxially grown, photovoltaic materials are eposited in stacked relation on a substrate in alignment with a coincident axis of input radiation impinging on a common optically active surface area of a detector device formed by the stacked layers. Semi-insulating layers space the radiation absorbing layers to electrically separate the signal outputs respectively produced in response to impinging radiation limited to separate and distinct wavelengths within a common spectral range as a result of the interrelationships between bandgap energy properties of the layer materials.
In a process of preparing an infrared sensitive photodiode comprising the eps of (1) forming by vacuum deposition an epitaxial layer of a semiconductor alloy material selected from the group consisting of PbS, PbSe, PbTe, PbS.sub.x Se.sub.1-x, PbS.sub.x Te.sub.1-x, PbSe.sub.x Te.sub.1-x, Pb.sub.y Sn.sub.1-y S, Pb.sub.y Sn.sub.1-y Se, Pb.sub.y Sn.sub.1-y Te, Pb.sub.y Sn.sub.1-y S.sub.x, Pb.sub.y Sn.sub.1-y S.sub.x Te.sub.1-x, Pb.sub.y Sn.sub.1-y Se.sub.x Te.sub.1-x, Pb.sub.z Cd.sub.1-z S, Pb.sub.z Cd.sub.1-z Se, Pb.sub.z Cd.sub.1-z Te, Pb.sub.z Cd.sub.1-z S.sub.x Se.sub.1-x, Pb.sub.z Cd.sub.1-z S.sub.x Te.sub.1-x, and Pb.sub.z Cd.sub.1-z 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) vacuum depositing Pb metal onto a portion of the epitaxial layer of semiconductor alloy material to form a non-Ohmic Pb metal contact; and (3) forming an Ohmic contact on another portion of the epitaxial layer of semicondcutor alloy material; the improvement comprising: after step (1) but prior to step (2), forming a layer of a lead halide selected from the group consisting of PbCl.sub.2, PbBr.sub.2, PbF.sub.2, and mixtures thereof on the epitaxial layer of semiconductor alloy material by exposing the epitaxial layer to vapor of the lead halide in the presence of a flow of oxygen-containing gas wherein (a) the lead halide vapor is produced by heating the solid lead halide at a temperature T.sub.1 wherein 200.degree. C..ltoreq.T.sub.1 .ltoreq.500.degree. C., (b) the epitaxial layer of semiconductor material is heated at a temperature T.sub.2 wherein 100.degree. C..ltoreq.T.sub.2 .ltoreq.300.degree.C. and wherein 100.degree. C..ltoreq.T.sub.1 -T.sub.2 .ltoreq.350.degree. C., and (c) wherein the oxygen-containing gas is selected from the group consisting of (i) air, (ii) oxygen, and (iii) a mixture of from 20 to less than 100 weight percent of oxygen and an inert dilutant gas which will not react with the lead halide, alkali metal halides, alkaline earth halides, or the semiconductor alloy material.
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 consisting 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-z 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 epitaxal 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 the 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 of 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 .ltoreq.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.
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.
