Hole density dependence of effective mass, mobility and transport time in strained Ge channel modulation-doped heterostructures

We performed systematic low-temperature (T=350 mK-15 K) magnetotransport measurements on the two-dimensional hole gas with various sheet carrier densities P-s=(0.57-2.1)x10(12) cm(-2) formed in the strained Ge channel modulation-doped (MOD) SiGe heterostructures grown on Si substrates. It was found that the effective hole mass deduced by temperature dependent Shubnikov-de Hass oscillations increased monotonically from (0.087+/-0.05)m(0) to (0.19+/-0.01)m(0) with the increase of P-s, showing large band nonparabolicity in strained Ge. In contrast to this result, the increase of the mobility with increasing P-s (up to 29 000 cm(2)/V s) was observed, suggesting that Coulomb scattering played a dominant role in the transport of the Ge channel at low temperatures. In addition, the Dingle ratio of the transport time to the quantum lifetime was found to increase with increasing P-s, which was attributed to the increase of remote impurity scattering with the increase of the doping concentration in MOD SiGe layers. (C) 2003 American Institute of Physics.