In-situ Observation of Atomic Layr Epitaxy by Photoelectron Oscillation

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Recently, we carried out real-time ultraviolet photoelectron spectroscopy (UPS) measurements using synchrotron radiation during Si epitaxial growth on a Si(100) surface by Si_2H_6 gas-source molecular-beam epitaxy (GSMBE), and observed that the normal emission intensity of the photoelectrons from the serface states on Si(100)2x1 oscillates periodically. We interpreted this photoelectron-intensity oscillation (PIO) as due to Si layr-by-layr growth, and showed a possibility of monitoring the epitaxial growth process by PIO.The purpose of this study is to elucidate the origin of PIO.The obtained results are described as follows.1.PIO and reflection high-energy electron diffraction (RHEED) oscillation were simulated by the Monte Carlo technique. PIO was reproduced well by a model assuming an alternation between the 2x1 and the 1x2 surface reconstructions during growth. The results of the simulation also showed that PIO appears under wide ranges of the temperature and of the growth rate com … More pared with those for RHEED oscillation.2.The model in result 1 consequently suggests that the period of the oscillations correspond to two monolayr growth. To confirm this relation, RHEED oscillation were measured during GSMBE,under identical growth conditions with those used for PIO observations. The oscillation period at the half-order diffraction spots agreed well with that of PIO at various Si_2H_6 pressures, providing a direct support for the above interpretation for the origin of PIO.3.Initial thermal oxidation processes by dry oxygen within the first monolaver on Si(100) have been investigated by real-time UPS.For oxidation temperatures at 350-600ﾟC the time evolution of the O 2p state intensity, a good measure for the amount of the formed oxide, presented a Langmuir-type adsorption behavior. For temperatures above 700ﾟC, the evolution was well described by a model assuming a twodimensional island growth. A unified explanation is given for this difference in the oxidation kinetics by considering the presence of the oxide decomposition process in the higher temperature region. Less