A study of high-purity CdxSe1−x vacuum-deposited thin films

Abstract

Pure CdSe films were vacuum deposited onto liquid-nitrogen-cooled substrates using a doubly baffled source in an attempt to prepare and study amorphous CdSe. The deposition of stable stoichiometric amorphous pure films was not verified since the films were always polycrystalline when analyzed at room temperature. CdSe appears to be different from some other II– VI compounds that can be prepared as pure stoichiometric amorphous materials and can be studied at a temperature up to 400 K. Pure nonstoichiometric films were also prepared using a second source to supply the excess component. Amorphous Se-rich films could only be produced for samples with at least 59 at.% Se. For Cd-rich films, the excess Cd agglomerates and the CdSe crystallite sizes are smaller than those observed in stoichiometric films. The electrical and optical properties scale as a function of the Cd content and the films become metallike as the Cd content increases through 60 at.%. The electrical transport properties are very different for polycrystalline films, depending on whether the CdSe is deposited on a hot substrate, or on a cold substrate and annealed to the same high temperature. We show that impure amorphous films of CdSe can be deposited if the system's background pressure is high.