Growth of the anodic sulfide film on Hg1−xCdxTe (MCT) by the potential step method into the electrochemical passivation region

The growth of the anodic sulfide film on Hg1−xCdxTe (MCT) by a potential step directly into the electrochemical passivation region is reported. Second harmonic generation (SHG) was employed to analyse the film during and subsequent to the growth. The analysis of the surface structure by SHG rotational anisotropy showed that the thin sulfide film formed by the potential step method did not lead to changes in the surface symmetry. However, increasing the film thickness by a voltage scan negative from the passive region led to an almost complete loss of the SH intensity which has been attributed to absorption of the fundamental and SH signals by the β-HgS present in the sulfide film. The anisotropy pattern of the film here showed strong deviations from the four-fold symmetry expected for the vicinal (1 0 0) surface. On the other hand, where current oscillations were observed during the cathodic voltage sweep from the passivation region, no reduction in the SH intensity was observed even for thicker sulfide films, signifying that the β-HgS had been removed from the layer. The close conformity in the anisotropy patterns between the original MCT surface and that for the sulfide-covered MCT surface confirms that the sulfide film is epitaxial, maintaining the ccp structure of the MCT substrate.