GROWTH OF NATIVE CADMIUM-SULFIDE FILMS ON CDXHG1-XTE FROM AQUEOUS SULFIDE SOLUTIONS

The anodic growth of native sulfide films from sodium sulfide aqueous solutions was carried out. The compositions of the layers are found to be dependent on the solution pH and on the electrochemical conditions employed for the growth. Current oscillations are observed during gro wth at potentials where the HgTe component of the CdxHg1-xTe (CMT) is oxidized in sulfide solutions of moderate strength. The solubility in excess sulfide of the HgS thus formed is found to be a critical compon ent in setting up these oscillations. The spontaneous growth of thick (ca. 2000 Angstrom) sulfide films on the CMT surface has been observed , and the process has been attributed to a photocorrosion-type reactio n. Ellipsometry and photocurrent measurements reveal that the sulfide films grown at controlled potential correspond closely to CdS (E(g) = 2.42 eV). The composition of the layers, examined by X-ray photoelectr on spectroscopy (XPS) and secondary neutral mass spectrometry (SNMS), also shows a surface enriched with HgTe, originating from the CMT subs trate. This has been confirmed by thermodynamic calculations based on the Gibbs energy minimization of the Cd-Hg-Te-S-O system, showing that HgTe can be in equilibrium with CdS, HgS, and CdSO4 on the sulfide la yersurface.