The mobility of electrons in strained silicon

Abstract

The development of Si and Si 1−xGe x layer growth by molecular beam epitaxy has enabled heterostructures and HEMT devices to be made with Group IV semiconductors. Strain is very important in determining the electronic behaviour of this system and as an initial step towards understanding mobility in SiGe HEMT structures a Monte Carlo technique has been used to simulate electron transport in bulk Si, strained by commensurate growth on a (001) Si 1−yGe y buffer. The in-plane mobility initially increases with increasing strain but then falls at higher strains and fields. Results are presented for both undoped and 10 17 cm −3 n-type Si, fields of 10 2 to 10 4 Vcm −1 and strain levels up to the equivalence of growth on a Si 0.25Ge 0.75 buffer. The results are explained by the splitting of the degenerate conduction band minimum and the transition probability between the two-fold and four-fold split minima.