Temperature dependence of transport properties of high mobility holes in Ge quantum wells

The transport properties of a two-dimensional hole gas (2DHG), with very high room-temperature drift mobilities, formed in 7.5- (2540cm2V−1s−1) and 20-nm (2940cm2V−1s−1) strained Ge quantum wells of multilayered Si∕Si0.33Ge0.67∕Ge∕Si0.33Ge0.67∕Si0.73Ge0.27∕Si(001) p-type modulation-doped heterostructures were investigated experimentally in the temperature range of 10–295K. For both samples the drift mobility of the 2DHG behaves in the same way as the Hall mobility, increases as the temperature decreases. The sheet carrier density of the 2DHG increases with decreasing temperature, which is opposite to the behavior of Hall-effect sheet carrier density. We found that the 2DHG formed in the thicker Ge quantum well has a higher drift mobility at 295K but a lower one at low temperatures. For both samples the Hall factor increases with decreasing temperature, reaching unity at 10K, when carriers in parallel conducting layers completely freeze-out. The interpretation of these results is carried out and the scattering mechanisms limiting the 2DHG mobility are discussed.