Chemical Treatment Effect of (001) GaAs Surfaces in Alkaline Solutions

Chemically treated (001) GaAs surfaces in aqueous alkaline solutions (NH4OH, KOH, and NaOH) at 17°C have been studied using spectroellipsometry, ex situ atomic force microscopy, and contact-angle measurement techniques. The spec-troellipsometry data clearly indicate that the solutions cause removal of the native oxide film immediately upon immers-ing the samples (t- 0.1 mm). The spectroellipsometry data also indicate that when the native qxide film is completely etch-removed, the resulting surface is still roughened. Tlhe estimated roughness thickness is —14 A, which is considerably larger than the atomic force microscopy rms value (—8 A); the difference is due to the spectroellipsometry technique being sensitive to both the roughened oxide/GaAs interlayer and the newly grown oxide film, while atomic force microscopy is sensitive only to the oxide/GaAs interlayer roughness. The contact-angle measurements suggest that the as-degreased GaAs surface is hydrophobic, while the chemically treated surface is hydrophilic. No clear difference in surface effects of the three alkaline solutions was observed