Upper Limit of Two-Dimensional Hole Gas Mobility in Ge/SiGe Heterostructures

Ge/SiGe heterostructures are promising candidates of future p-type FETs. The two-dimensional hole gas (2DHG) formed in the strained Ge layer has high hole mobility because the modification of the band structure by the lattice mismatch leads to reduction in the effective mass and suppression of the interband scattering. Up to now, the highest 2DHG mobility obtained experimentally with the Ge/SiGe heterostructure is 3100 cm2/Vs for room temperature. This hole mobility is about 150% and 700% more than those in bulk Ge and Si, respectively. However, the theoretical limit of 2DHG mobility in the Ge/SiGe heterostructure has not been established due to the experimental challenge of measuring purely the 2DHG mobility in Ge/SiGe heterostructures and theoretical challenge of modeling it with the anisotropy and nonparabolicity of the valence band included appropriately. Here we present experimental and theoretical investigations of 2DHG mobility in Ge/SiGe heterostructures and deduce the theoretical limit of 2DHG mobility as a function of the strain in Ge.