Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS)
were used to investigate interdiffusion and surface properties of CdS/CdTe
bilayers. The films were grown by radio-frequency sputtering and received p
ostdeposition heat treatments similar to the ones employed in CdTe solar ce
ll fabrication. It is found that a CdCl2 anneal strongly enhances both the
diffusion of S into the CdTe layer and the surface oxidation. The diffusion
of S in CdTe in this process can be described by a constant surface source
model with the diffusivity given by D = 3.2 x 10(-5) exp(-1.2 eV/kT) cm(2)
s(-1) in the temperature range studied. The change in the chemical composi
tion of the surface following the CdCl2 anneal was analyzed by XPS showing
that Te oxides and residual compounds containing Cl were present which coul
d account for the straggling in the RBS spectrum. An HCl etch completely re
moves oxides and residues leaving a smooth surface. (C) 2000 American Insti
tute of Physics. [S0021-8979(00)05704-2].