Carrier freeze-out in strained p-Si1-xGex layers

In this paper, the carrier freeze-out in strained p-Si_1-x Ge_x layers grown on (001) substrates is studied analytically. It is found that as the Ge fraction increases, the valence effective density of states (N_V)_SiGe/(N_V)Si normalized by that in Si decreases. Furthermore, as the temperature becomes lower, the decrease in (N_V)_SiGe/(N_V)Si becomes more rapid. It is also show that as the Ge fraction increases, although it has little effect on the ionized doping concentration at room temperature, the ionized doping concentration increases at low temperatures compared with that in Si. This implies that carrier freeze-out is mitigated at low temperatures, which can have a beneficial effect on the operation of Si_-xGe_x-based devices at low temperatures