Abstract: A photo diode formed by a substrate of Cd.sub.x Hg.sub.1-x Te covered with a layer of CdTe forming a p-n junction. The substrate may be p-type in which case the layer is n-type or vice versa. An array of photo diodes may be formed by covering the substrate with semi-insulating CdTe and forming islets of In on the CdTe. Heating causes In to diffuse into the CdTe doping it n-type. This results in regions of n-type CdTe surrounded by semi-insulating CdTe each region forming, with the substrate, a photo diode. The heating also causes diffusion between the Cd.sub.x Hg.sub.1-x Te and CdTe to give a graded heterostructure. Electrical connections are made to the substrate, and each n-type region. The n-type CdTe region may alternatively be formed by molecular beam epitaxial growth techniques using a beam of In dopant.

Abstract: A semiconductor device (1) including a monocrystalline region of semiconductor grey tin material (5) in intimate contact with a monocrystalline substrate (3). The region of semiconductor tin (5) is stabilized by interaction with the monocrystalline substrate (3) which has a crystallographic structure isomorphous with the structure of grey tin and an interatomic spacing matched to the interatomic spacing of the semiconductor region (5). The semiconductor region (5) may be further stabilized by inclusion of germanium dopant. The matching substrate (3) may be of indium antimonide, cadmium telluride, germanium or silicon material. Ohmic contact between a region of semiconductor tin (5) and a region of metal white tin (15) may be formed. Details of infra-red photovoltaic and photoconductive devices are given.The semiconductor region of tin may be grown by molecular beam epitaxy.

Abstract: An FET device comprises a substrate with source and drain regions separated by a gate structure. Between the gate and substrate is an insulator formed of a cubic fluorite structure material that is lattice matched within 1% to the substrate. The insulator may be a group II fluoride such as Ca.sub.y Cd.sub.1-y F.sub.2 (0.ltoreq.y.ltoreq.1), Sr.sub.z Ba.sub.1-z F.sub.2 (0.ltoreq.z.ltoreq.1), or Ba.sub.x Ca.sub.1-x F.sub.2 (0.ltoreq.x.ltoreq.1), or an oxide such as CeO.sub.2, PbO.sub.2. The substrate may be a bulk semiconductor or an epitaxial layer such as Si, InP, GaAs, Ga.sub.x Al.sub.1-x As, GaSb, InAs, or AlAs.