Surface cleaning and etching of CdZnTe and CdTe in H2/Ar, CH4/H2/Ar, and CH4/H2/N2/Ar electron cyclotron resonance plasmas |
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Authors: | Robert C. Keller H. Zimmermann M. Seelmann-Eggebert H. J. Richter |
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Affiliation: | 1. Fraunhofer-Institut für Angewandte Festk?rperphysik, 79108, Freiburg, Germany
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Abstract: | This paper compares H2/Ar, CH4/H2/Ar, and CH4/H2/N2/Ar plasma etch processes for CdZnTe and CdTe substrates in view of their potential to provide high-quality substrate surfaces for subsequent HgCdTe epitaxy. An electron cyclotron resonance source was used as plasma generator, and ellipsometry, angle-resolved x-ray photoelectron spectroscopy and low energy electron diffraction were applied to characterize roughness, composition, and order of the resulting substrate surfaces. It was found that CdZnTe is much more susceptible to evolving surface roughness under H2/Ar plasma exposure than CdTe. The severe roughening observed at 100°C sample temperature was found to be correlated with a buildup of ZnTe at the surface, which suggests that the roughness formation may result from a preferential etching of the CdTe component. This surface degradation could be reduced by the addition of CH4 to the process gases. However, only a further addition of nitrogen gas balanced and substantially improved the plasma process so that atomically clean, very smooth, and stoichiometrically composed CdZnTe surfaces of long-range order were eventually obtained. |
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Keywords: | CdZnTe substrate cleaning electron cyclotron resonance (ECR) plasma etching HgCdTe epitaxy long wavelength infrared devices |
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