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

本文从原子尺度上研究了气固界面上外延薄膜生长的动力学过程，如反应组分的表面迁移和原子的表面偏聚，并提出了控制表面反应的方法，明确了Ar^+激光辐照对气体源分子束外延Si/Si和Ge/Si外延生长过程的影响。由于Si_2H_6和GeH_4分子不受Ar ^+激光的激发或离解，因此我们可以检测到表面激发对Ar^+激光辐照生长过程的影响。实验中观察到的特征是生长速率的增加和衬底温度的降低，反射高能电子衍射（RHEED）的强度振荡消失。生长速率的增加可以解释为由于吸附在表面上的氢原子的光解吸而增加了反应物种的吸附位点。RHEED强度振荡的消失意味着吸附氢的光脱附增强了表面原子的迁移，从而促进了台阶流动生长.本文还研究了Si/Ge_n/Si系统中Ge原子的表面偏聚，其中n从1变化到6.结果表明，与常规MBE相比，气源MBE中表面Ge浓度的衰减长度降低了1/2-1/8，表面偏析的机理可用双位交换模型解释，并认为表面悬键被氢原子终止降低了表面偏析引起的自由能的明显变化。阐明了氢原子在表面迁移、表面偏析等动态表面反应过程中的作用以及控制表面反应的可能性。

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.