While several factors enter the final rate equation for defect charge capture rates, it is predominantly the vibrational overlap between PES and the corresponding thermal population in the initial charge state which determines the overall rate. The connection between these PES and the capture cross-sections s e/h can thus be intuitively understood by considering the classical energy barrier to the transition (indicated by DE e/h in Fig. ), upon which the capture rate is inverse-exponentially dependent, due to the exp( E/k B T ) Boltzmann population factor for the overlapping states. If no classical barrier exists (i.e. e(0/ 1) & e(0 ⇤ / 1)), then charge capture proceeds primarily via quantum tunnelling, with weak temperature dependence as seen in the cross-sections in Fig. .