Fig. 3: The schematic of phonon-assisted tunneling and hopping transport dynamics.
Charge carriers that initially fall into ultra-shallow trap states are; (I) de-trapped on to the conduction band (Ec) via tunneling before slowly recombining, (II) relax into slightly deeper ultra-shallow states and de-trapped again, (III) “hop” between shallow trap states. Only electron motion is demonstrated in the model since holes follow the same mechanism. The zero-time point is set at 10% of maximum photocurrent. Note: to clarify the transport process and for convenience only some of the typical states existing within each region are shown. Whereas in the actual case trap levels in the regions between 0 and 2000 ps are continuous as seen in Fig. 2. The valance band is depicted by Ev.
