Development of a time-resolved measurement method for detecting surface dynamic processes of epitaxial growth and studies on surface migration of reaction species.

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The purpose of this work is to study dynamic processes of epitaxial film growth at gas-solid interfaces in an atomistic scale, such as surface migration of reaction species and surface segregation of atoms, and to develop a method for controlling surface reaction.It has been made clear the influence of Ar^+ laser irradiation in growth processes for epitaxial growth of Si/Si and Ge/Si by gas source molecular beam epitaxy. We can detect an effect of surface excitation on growth processes by Ar^+ laser irradiation because Si_2H_6 and GeH_4 molecules are not excited or dissociated by Ar^+ laser light. Characteristic features observed in this experiment are an increase in growth rates and a lowering of the substrate temperature that the intensity oscillation of reflection high energy electron diffraction (RHEED) is vanished. The increase in growth rates can be explained by an increase in adsorption sites of reaction species due to photo-desorption of hydrogen atoms adsorbed on surfaces. The vanishment of the intensity oscillation of RHEED means that the growth by step flows is promoted by an enhancement of surface atomic migration due to the photo-desorption of adsorbed hydrogen.The surface segregation of Ge atoms in Si/Ge_n/Si systems is also examined, in which the n is changed from 1 to 6. It can be found that a decay length of surface Ge concentrations in gas source MBE is lowered by 1/2-1/8 compared with that in conventional MBE.The mechanism of surface segregation is explained by the two-site exchange model, and it is considered that an apparent change in free energy due to segregation is lowered by the termination of surface dangling bonds with hydrogen atoms.In conclusion, we can clarify the role of hydrogen atoms on dynamic surface reaction processes such as surface migration and surface segregation and the possibility of controlling the surface reaction.