Vacuum Deposition of Stoichiometric Thin Films of II-VI Sulphide Semiconductors.

Abstract: Compound semiconductors provide a large range of materials with varying band gaps for application in devices. Usually these devices are made in the form of thin films, whose crystalline quality and stoichiometry play a pivotal role in the stability and the performing characteristics of the device. Vacuum deposition of thin films is the most popular and dependable method of preparing thin films. However, it is a general problem that the compound semiconductors thermally dissociate into their constituent components during evaporation. To overcome this difficulty, we optimize a method, wherein good quality films of sulphide semiconductors were grown by using a low ambient H2S atmosphere inside the vacuum chamber while thermally evaporating the sulphide semiconductor materials. The substrate was kept at an elevated temperature, which was high enough for the dissociated sulphur ions to be ejected from the substrate while the dissociated metallic cations quickly combined with the highly reactive H2S molecules to get deposited as sulphide molecules. Such films naturally had better stiochiometric ratio, better crystallinity, and had less structural defects. Such films were remarkably pin hole free and had better adhistivity with the substrates. Such films would be inherently more suitable for any electro-optical devices. [Copyright &y& Elsevier]