SURFACE CLEANING AND ETCHING OF CDZNTE AND CDTE IN H-2 AR, CH4/H-2/AR, AND CH4/H-2/N-2/AR ELECTRON-CYCLOTRON-RESONANCE PLASMAS/

This paper compares H-2/Ar, CH4/H-2/Ar, and CH4/H-2/N-2/Ar plasma etch processes for CdZnTe and CdTe substrates in view of their potential t o provide high-quality substrate surfaces for subsequent HgCdTe epitax y. An electron cyclotron resonance source was used as plasma generator , and ellipsometry, angle-resolved x-ray photoelectron spectroscopy an d low energy electron diffraction were applied to characterize roughne ss, composition, and order of the resulting substrate surfaces. It was found that CdZnTe is much more susceptible to evolving surface roughn ess under H-2/Ar plasma exposure than CdTe. The severe roughening obse rved at 100 degrees C sample temperature was found to be correlated wi th a build-up of ZnTe at the surface, which suggests that the roughnes s formation may result from a preferential etching of the CdTe compone nt. This surface degradation could be reduced by the addition of CH4 t o the process gases, However, only a further addition of nitrogen gas balanced and substantially improved the plasma process so that atomica lly clean, very smooth, and stoichiometrically composed CdZnTe surface s of long-range order were eventually obtained.