A plate of a semiconductor having a narrow energy gap such as InSb, is applied with a magnetic field in parallel therewith and further supplied with a current in parallel therewith also as well as across the magnetic field, whereby an infrared radiation can be emitted perpendicular thereto in a wide range of temperature from room temperature to liquid nitrogen temperature. Consequently, an infrared emitting device, for instance, an infrared laser diode can be fabricated and operated at room temperature without necessity of a dewar filled with refrigerating material such as liquid nitrogen. Various kinds of compact infrared-emitting equipments such as an infrared radar can be realized by modulating the current supplied to the above infrared emitting device.

Optical detectors used for remote controls must be able to function over long distances and under various environmental conditions. They must therefore have a high sensitivity, which means they also respond to electrical and magnetic inference fields. The present optical detector avoids the need of being packed in an assembly, which has an additional internal metal shield for protection against electromagnetic interference. In this optical detector, the surface is coated with polysilicon, except for the top-lying cathode contact. Furthermore, a thick oxide layer is arranged between the substrate and the polysilicon coating, which is contacted to a highly p.sup.+ -doped region of the substrate. Such optical detectors, which are not subject to electromagnetic interference, are primarily required for remote controls.

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.