The drift mobility of electrons and holes in germanium at low temperatures

Abstract

The drift mobility of electrons and holes has been measured in the temperature range from 20°K to 300°K in samples of germanium containing impurity concentrations from 7 × 10 12 cm −3 to 4 × 10 15 cm −3. Conductivity measurements were also made. Below about 100°K the observed minority carrier mobility is less than the mobility calculated from the effects of scattering by phonons and ionized and neutral impurity atoms. The discrepancy, which is greater than a factor of 2 in some circumstances, has been attributed to electron-hole scattering. It is proposed that the unexpectedly large effect of electron-hole scattering is due to a drag exerted on the minority carriers by the majority carriers when an electric field is applied. Qualitative observations on the drift mobility of electrons have been made below 20°K. There is no evidence that electrons remain localized about the same minimum in k space for the duration of a transit time ( 1 2 μsec) . An extreme example of conductivity modulation of the injected distribution of carriers has been observed to occur when impact ionization is taking place.