Properties of GaP(001) surfaces chemically treated in NH4OH solution

Chemically cleaned GaP(001) surfaces in 25% NH4OH solution have been studied usingspectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectronspectroscopy (XPS), and wettability measurement techniques. The SE data clearly indicate that thesolution causes removal of the native oxide film immediately upon immersing the sample. The SEdata also indicate that when the native oxide film is completely etch removed, the resulting surfaceis still roughened. The estimated roughness thickness is 1.2 nm, in excellent agreement with theAFM rms value (1.2 nm). The XPS spectra confirm the removal of the native oxide from the GaPsurface. The XPS data also suggest a thin oxide overlayer, 0.3 nm thick, on the etch-cleaned GaPsurface. The wettability measurements indicate that the as-degreased surface is hydrophobic, whilethe NH4OH-cleaned surface is hydrophilic. This result is in direct contrast to those obtained fromacid cleaned surfaces, which are usually hydrophobic. The origin of hydrophilicity may be singularand associated hydroxyl groups bonded on the GaP surface