Sheng Chi

Energy Levels of Valence Subbands in Si/Si1-xGex Quantum Well by Admittance Spectroscopy

Using the admittance spectroscopy technique, energy levels of subbands in SiGe/Si quantum well are studied. The value of activation energy increases with increasing well width, in accordance with the quantum confinement effect. Two conductance peaks due to hole emission from heavy hole ground state and light hole ground state were observed. It was found that the value of activation energy increased with annealing time at the temperature of 800° C, while the activation energy decreases with the annealing time at 900° C.

Ge BEAM TREATMENT OF Si SUBSTRATE FOR MOLECULAR BEAM EPITAXY

A new surface cleaning method for Si MBE is described in which a very weak Ge beam flux is deposited on the surface for removing the thin passivative layer of SiO2 on the Si substrate. It has proved that the SiO2 will react with Ge at a relatively low temperature (620° C), and as a result, the oxide layer becomes volatile. Here the high temperature annealing in the conventional Shiraki method is no longer required, and since the oxide layer is removed in ultra high vacuum, only very little carbon contamination may occur. Furthermore, to reduce the excessive Ge on the substrate surface, Ge is deposited at 620° C and then the sample is annealed at 700° C; the residual Ge atoms on Si substrate can be reduced to less than 0.1 monolayer (ML). Ge beam treatment turns out to be an effective low-temperature Si surface-cleaning method, especially for the heteroepitaxial growth of GexSi1-x/Si.