Surface films on HgCdTe and CdTe etched in ferricyanide solution

Surface films are obtained on Hg0.79Cd0.21Te and CdTe by treatment in a solution of 0.1 M Fe(CN)63− (ferricyanide) in 0.5 M KOH. Composition profiles are obtained by X-ray photoelectron spectroscopy (XPS), and they reveal the presence of cadmium oxide (CdO) and elemental tellurium (Te0). The film on Hg0.79Cd0.21Te is porous and thick (e.g. 800 Å), whereas the film on CdTe is nonporous and thin (<100 Å). The presence of CdO instead of Cd(OH)2 and the presence of Te0 despite the highly oxidizing Fe(CN)63− ions are not predicted by equilibrium thermodynamics; they are due to the film growth kinetics. The origin of the surface chemical films is discussed in detail.