Radiative-tunnel hopping diffusion of electrons over a system of F-centres in pre-breakdown electric fields in ionic crystals - theoretical approach

One can also compare these τRTT ´s with the rate of direct field ionization of an F´-centre. The theory developed in [8] gives for the characteristic ionization time of a particle trapped in a delta-well of the effective strength γ, the following order-of-magnitude estimate: equation where E0 = 5.142 × 10⁹ V/cm is an atomic unit of an electric field (equation). For E = 1 MV/cm and γ⁻¹ = 1.89 Å, eq. (6) gives a very large value τioniz ≃ 1.65 × 10¹⁹ sec, i.e., direct ionization of F ´-centre for these parameters is a very small effect. It should be noted, however, that eq. (6) is very sensitive to the values of γ⁻¹ and E and a moderate increase of E can make the direct field ionization comparable with inter-site RTT jumps considered above.