Low‐Temperature Conductivity and Mobility in Semiconductors

The influence of the free‐carrier concentration upon the low‐temperature conductivity is investigated. The variation may be due either to temperature effects (under thermal equilibrium conditions) or to the influence of an electric field (under non‐equilibrium conditions). The effect considered is significant up to the temperature at which the free‐carrier concentration saturates and for the thermal electrons at low compensation ratio. Then the low‐temperature conductivity considered as a function of the temperature and electric field strength acquires a sharp minimum while the maximum of the conductivity becomes higher and shifts towards lower temperatures and smaller fields. The comparison with experimental data shows quite a good agreement between the experimental and theoretical curves. This suggests that the mobility minimum which for rather a long time was being observed and not understood is due to the effects discussed above. The cascade electron capture cross‐section of the ionized donors is re‐calculated using the sticking probability corrected by Abakumov and Yassevich. The result is used to calculate the capture coefficient in a strong electric field.