Time-resolved hole transport ina−SiO2

The transport of excess holes in amorphous Si${\mathrm{O}}_2$ is reported as a function of field and temperature, with an emphasis on the behavior at short times ($t\ge 10$ nsec) after the hole is introduced into the glass. The unusual features of the transport for $t\gtrsim {10}^{-5\mathrm{}}$ seconds can be rationalized on the basis of the continuous-time random-walk model (CTRW) of Scher and Montroll. It is hypothesized that at short times the hole hops, perhaps as a small polaron, from one oxygen nonbonding orbital to one of the nearest-neighbor oxygen orbitals. The hole is eventually trapped at a structural defect and the transport continues as a tunneling from one defect to another, causing the unusual transport phenomena associated with the CTRW. The temperature dependence of the hole transport is markedly non-Arrhenius below 200°K, which is consistent with the small-polaron model.