Vapor phase deposition of cadmium and mercury telluride for electronic

Abstract

Alternate layers of CdTe and HgTe are deposited on a substrate in a reaction zone inside a reactor vessel using a method involving the steps of (a) passing a gas stream containing a volatile tellurium compound (Et.sub.2 Te) over the substrate while maintaining an atmosphere of mercury vapour in the reaction zone, and (b) switching on and off a separate supply of a volatile cadium compound (Me.sub.2 Cd) to the reaction zone so as to deposit CdTe when the separate supply is on and to deposit HgTe when the separate supply is off (O). The surface of the substrate is irradiated with electromagnetic radiation (UV) the intensity of which is switched during the deposition. The irradiation intensity (UV) is reduced, possibly even to zero (0), when the supply of the volatile cadium compound (Me.sub.2 Cd) is switched on. When the cadium supply (Me.sub.2 Cd) is switched off (O), the irradiation intensity (UV) is increased to promote photodissociation of the volatile tellurium compound (Et.sub.2 Te) by the electromagnetic radiation (UV). This permits the layers to be grown at a low substrate temperature, while avoiding premature nucleation of CdTe in the gas stream. The switching of the radiation intensity (UV) may be effected using a mechanical shutter to switch off (O) the irradiation (UV) or using an adjustable iris or movable neutral-density filter to reduce the UV intensity. The alternate layers may be interdiffused during growth to form a cadmium mercury telluride layer for an electronic device, for example an infrared detector or a bipolar transistor. Alternatively, the alternate HgTe and CdTe layers may be preserved in the final device, for example as a 'superlattice'.