Anodic sulfide films on HgTe and Cd0.24Hg0.76Te studied by in-situ ellipsometry

Abstract

The growth of anodic sulfide films on HgTe and Cd _x Hg _1-x Te (CMT) from aqueous sulfide solution is examined using in-situ ellipsometry. The dominating feature at low overpotentials for the HgTe is the dissolution of the substrate whereas for CMT it is the CdS film formation. The HgS film that eventually forms on the HgTe substrate at higher overpotentials maintains the ccp «111» orientation of the substrate and can be regarded as epitaxial. Electrochemical passivation of the CMT and HgTe surfaces is attributed to a change in the HgS surface film structure from ccp to hcp, triggered by the electric field across the film. The current oscillations that follow the passivation peak are due to the competing reactions of electrochemical formation and chemical dissolution of the β-HgS layer. Films grown to potentials beyond the passivation potential on the HgTe surface lose the epitaxial characteristic and smaller crystallites result, with mixed hcp and ccp orientation for the HgS, as observed from XRD measurements.