During the mean surface residence time measurements by means of molecular beam relaxation method it is often found that an error starts to appear as the mean residence time becomes comparable to the molecular beam modulation period. An analysis has been made to clarify that this is due to a systematic error which occurs during data processing using Fast Fourier Transform software. Fourier transform is usually performed in a single period of the desorbed molecular beam time-of-flight signal, while the resultant signal is a sum of the signals at present period and those initiated in the past periods. This signal overlapping creates a systematic error especially at high frequency components of Fourier transform.
Oxidation of GaAs surfaces in deionized water has been investigated by using X-ray photoelectron spectroscopy with respect to the influences of dissolved oxygen, illumination intensity, carrier types, and carrier concentration. Illumination greatly accelerates the oxidation of the GaAs surface. The dissolved oxygen concentration also affects the oxidation rate; oxidation becomes dominant over dissolution of oxides for the dissolved oxygen concentration of more than 1 ppm. The carrier type as well as the carrier concentration is a determining factor of oxidation rate. The hole concentration at the GaAs surface is considered to affect the oxidation rate.