Formation Conditions and Structure of Ge Films Deposited on Polished (111) CaF2 Substrates in an Ultrahigh-Vacuum System

Abstract

The structure of Ge films deposited over a wide range of deposition rates and substrate temperatures onto hand-polished (111) CaF2 substrates in a vacuum of 10−9 to 4×10−7 Torr has been characterized. The epitaxial temperature and the amorphous to crystalline transition temperature were found to be rate dependent. The linear relation observed between the logarithm of the deposition rate and the reciprocal of the epitaxial temperature agrees generally with nucleation theory of small clusters and yields an activation energy of 1.43 eV. The observed linear relation between the logarithm of the deposition rate and the reciprocal of the amorphous to crystalline transition temperature has been interpreted in terms of simple surface diffusion theory and leads to an activation energy for surface diffusion of Ge on CaF2 of 1.53 eV.