Properties of GaP(001) surfaces treated in aqueous HF solutions

Chemically cleaned GaP(001) surfaces in aqueous HF solutions have been studied using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), wettability, and photoluminescence (PL) measurements. The SE data clearly indicate that the solutions cause removal of the native oxide film immediately upon immersing the sample (?1 min). The SE data, however, suggest that the native oxide film cannot be completely etch-removed. This is due to the fact that as soon as the etched sample is exposed to air, the oxide starts to regrow. The SE estimated roughness is ～1 nm, while the AFM roughness value is ～0.3 nm. The XPS spectra confirm the removal of the native oxide and also the presence of regrown oxide on the HF-etched GaP surface. The wettability measurements indicate that the HF-cleaned surface is hydrophobic, which is in direct contrast to those obtained from alkaline-cleaned surfaces (hydrophilic). A slight increase in the PL intensity is also observed after etching in aqueous HF solutions

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

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