Electronic transport properties of thin, channel regions from SOI through GOI: A first-principles study

To investigate transport properties of the channel region in silicon on insulator (SOI) and germanium on insulator (GOI), we studied the electronic structure of hydrogen-terminated Si(100), (111) and (110), and Ge(100) and (111) slab models by the density functional theory. It is found that the electronic properties around 30 nm thickness are almost the same for those of the bulk and they deviate from the naive effective mass approximation theory in the range thinner than 4 and 10 nm for Si and Ge, respectively. The effective masses in the Si <001 > and Ge < 111 > confined models are almost constant and equal to the bulk ones throughout the calculated range. However, the masses of the other models strongly depend on layer thickness. These behaviors are related to the off-diagonal terms in the effective mass tensors. In the Ge < 100 > model, we found that the confinement causes the exchange of the conduction band bottom between the Γ and the Brillouin zone boundary, which may cause the enhancement of the electron mobility.