Temperature dependence of charge carrier mobility in single-crystal chemical vapour deposition diamond

Abstract

Measurements of the temperature dependence of the charge carrier mobility in single-crystal chemical vapour deposition diamond using the transient current technique are presented in a temperature range from 2 K to room temperature. An α-source is used to create free charge carriers in the diamond bulk. The evolution of the current signal induced by their drift under the influence of an externally applied field is studied as a function of the temperature and the electric field strength. The electric field strength is varied by a factor of 30. The measurements are used to extract the transit time, the drift velocity, the saturation velocity, and the low-field mobility in terms of which the results are interpreted. Three samples have been studied which show the same behaviour. For holes, the mobility increases with decreasing temperature due to the acoustic phonon scattering, but it saturates for ultra-cold temperatures. The low-field mobility for holes at room temperature is measured as μ0h(295K)=(2534±20) cm2/Vs saturating against μ0h(→2K)=(11130±120) cm2/Vs. For electrons, only a lower limit on the low-field mobility can be given. It is measured as μ¯0e(295K)=(1802±14) cm2/Vs saturating against μ¯0e(→2K)=(3058±27) cm2/Vs. The electron transit time at low fields shows a different behaviour than the hole transit time and is not following the expected behaviour. This is likely to be caused by a high temperature valley re-population effect.