Monte Carlo simulation of hole transport in strained Si_{1 - x}Ge_x

The transport properties of holes in Si_{1 - x}Ge_x are studied with a Monte Carlo technique. If the strain is applied to the Si_{1 - x}Ge_x channel, it raises the degeneracy of the heavy-hole and light-hole bands: for compressive strain, the heavy-hole band lies at a higher energy than the light-hole band, while for tensile strain, the order reverses, although it is technologically uncertain how to realize the tensile case at this stage. The transport properties are essentially the same for the unstrained and compressive cases, since most holes are in the heavy-hole band over the entire field range of interest. Although the overshot is negligible, the hole velocity is still higher than that of Si, reflecting the excellent hole transport properties in Ge. In the tensile case, we have observed a negative differential resistance region for 5 × 10²-5 × 10³V/cm, due to the hole transfer from the light-hole band to the heavy-hole band. The velocity is much larger than that of compressive or unstrained cases, especially at low fields. Because of the small effective mass in the light-hole band, the velocity overshoot is significant in the tensile strain case. These results provide motivation to try to realize the tensile strain case technologically.