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

在分子束外延系统中，通过铂和硅的共蒸发，在Si(111)表面上生长的PtSi层比在Si(001)表面上生长的PtSi层更完美。当衬底温度在400ﾟC或以下时，在PtSi层上外延生长了Si，得到了Si/PtSi/Si双异质结构。然而，当Si生长的衬底温度为600ﾟC或以上时，PtSi和Si反应生成柱状结构。为了在p-Si/Ge/Si应变超晶格中形成陡峭的界面，研究了B作为p型表面活性剂的作用。HBO_2被用作B源，因为它比元素B本身具有更高的蒸汽压。研究发现，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B吸附大于1/3单分子层(ML)的Si(111)表面外延生长时，RHEED振荡周期是B吸附小于1/3ﾟ的Si衬底上的两倍。从周期变化的位置可以估计，在450mLC的Si生长温度下，B的偏析长度为14A，它随着衬底温度的升高而迅速增加，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Si/Ge/Si应变超晶格的实际表面活性剂效应。

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.