Study of GaAs(001) Surfaces Treated in Aqueous HCl Solutions

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Abstract
Chemically treated GaAs(001) surfaces in aqueous HCl (0.36≤x≤36 wt%) solutions at 20° C have been studied using spectroellipsometry (SE), ex situ atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact-angle measurement techniques. The SE data clearly indicate that the solutions cause the removal of the native oxide film. When the native oxide film is etch-removed, the resulting surface is still rough (∼8 Å). Longer exposure to the solutions with x≤12 wt% results in surface roughening; the thickness of the roughened layer immersed in the solution with x=3.6 wt% for t=100 min, for example, is ∼60 Å, about twice as large as the AFM rms value (∼27 Å); the difference is due to the SE technique being sensitive to both the surface microroughness and the adsorbed chemical species. By contrast, the concentrated HCl (36 wt%) etching provides a nearly flat (AFM rms of ∼7 Å), Cl-terminated surface even after considerable etching. The XPS spectra clearly indicate the presence of chlorine on the HCl-treated surfaces. The HCl-cleaned GaAs surfaces are also found to be highly hydrophobic.