Deposition and growth with desorption for CdTe molecular beam epitaxy

Abstract

It is well known that during epitaxial growth of thin films of almost all II–VI semiconductors, the growth rates show a pronounced temperature dependence which is due to desorption of one or both components from the growing surface. The measured desorption rate appears to be thermally activated with a strikingly small value: a few tenths of an eV. The explanation generally put forward is that the desorption of a weak-binding state acts as a “precursor” to chemisorption. According to this point of view, the small measured activation energy is a real energy corresponding to a well-defined microscopic process. We argue that no weak-binding precursor state is needed for reproducing the experimental growth rate of CdTe. Using Burton, Cabrera and Frank's theory and by performing Monte Carlo simulations of a one-particle model for deposition, diffusion, aggregation and desorption, we have found that the macroscopic desorption rate appears to be thermally activated over a large range of temperatures. This rate is a combination of all the microscopic energies — diffusion barrier and desorption barrier — and it can take values of a few tenths of an electronvolt, even though all microscopic energies are much larger. A very simplified model of CdTe growth is thus proposed and tested against experimental measurements of growth rates for various temperatures and deposition fluxes