Dissolution of arsenic and gallium oxides on GaAs surface during running deionized water (RDIW) and ultrasonic-running deionized water (U-RDIW) treatments is investigated by X-ray photoelectron spectroscopy (XPS). The U-RDIW treated (001) GaAs surfaces are also investigated by reflection high-energy electron diffraction (RHEED). The deionized water used in these treatments is thoroughly deoxygenated to less than 0.3 ppm by bubbling nitrogen gas. RDIW treatment removes arsenic oxide more rapidly than gallium oxide. U-RDIW treatment accelerates the removal of both oxides from GaAs surface and produces oxide-free GaAs surface within 1 hr. After U-RDIW treatment, RHEED observation of the acid-etched surfaces shows a spotty (1×1) pattern at room temperature and a (2×1) streaky reconstruction pattern at 360 C. Ammonium-etched surfaces, on the other hand, show a (2×4) streaky reconstruction pattern at 310 C. The experimental results indicate that chemically-clean and damage-free GaAs surfaces can be produced by U-RDIW treatment. They also show that As/Ga ratios between the acid- and ammonium-etched GaAs surfaces after the U-RDIW treatment are different.
The thermal oxidation of silicon at lower temperature by using dinitrogen monoxide (N2O) gas and UV-irradiation has been investigated. A low pressure mercury lamp is used as light source. Silicon can be oxidized thermally at 300°C. The main oxidizing species are the atomic oxygen O(1D) which is created by the dissociation of N2O during UV-irradiation. Oxide thickness is 4.7 nm at 500°C for 4h oxidation. It is clear from AES analysis that the composition of silicon and oxygen atom in the film formed by the present technique is same as that formed by high temperature oxidation in common dryO2 ambient. High frequency C-V characteristics for the film in the present technique is better than that in common dryO2 oxidation.