Preparation and properties of Hetero-junctions between PtSi or p-Si and p-Si/Ge strained superlattice

通过在MBE体系中Pt和Si的共蒸发，发现PtSi层在Si（111）表面的外延生长比在Si（001）表面的外延生长更完美。当衬底温度为400℃或更低时，Si在PtSi层上外延生长，得到Si/PtSi/Si双异质结构。而当Si生长的衬底温度在600℃以上时，PtSi与Si发生反应，形成柱状结构。为了在p-Si/Ge/Si应变超晶格中形成突变界面，研究了硼(B)作为p型表面活性剂的作用。采用HBO_2作为B源，是因为它比元素B本身具有更高的蒸气压。通过观察B吸附表面的RHEED强度振荡，可以控制B的亚单层吸附。当Si在Si（111）表面外延生长且B吸附量大于1/3单分子膜（ML）时，其振荡周期是在吸附量小于1/3单分子膜（ML）的Si衬底上生长时的两倍，从周期变化的位置可以估计出，在Si生长温度为450℃时，B的偏析长度为14A。随着Si - MBE生长的衬底温度的升高，它迅速增加，因此，B被认为是一种很有前途的p型表面活性剂。目前正在研究表面活性剂对Si/Ge/Si应变超晶格的实际作用。

PtSi layrs were found to be grown epitaxially on Si (111) surface more perfectly than on Si (001) surface by co-evaporation of Pt and Si in a MBE system. When the substrate temperature was 400ﾟC or below, Si was epitaxially grown on PtSi layr and Si/PtSi/Si double-hetero structure was obtained. However, PtSi and Si reacted and made columnar structures when the substrate temperature of Si growth was 600ﾟC or above.In order to make an abrupt interface in a p-Si/Ge/Si strained super lattice, Boron (B) was investigated as a p-type surfactant. HBO_2 was used as the B source since it has a higher vapor pressure than elemental B itself. It was found that sub-monolayr adsorption of B could be controlled by observing the RHEED intensity oscillation of B absorved surface. When Si was epitaxially grown on Si (111) surface where the B was adsorbed more than 1/3 monolayrs (ML), period of the RHEED oscillation was twice of that for growth on the Si substrate where the B was adsorbed less than 1/3 ML.From the position where the period changes, segregation length of B could be estimated to be 14A at Si growth temperature of 450ﾟC.It increased rapidly with increase of the substrate temperature of the Si MBE growth, therefore, B is believed to be a promising p-type surfactant. Actual surfactant effect for a Si/Ge/Si strained super lattice is presently being studied.