The Transport Process of Photo-Induced Carriers in Rutile

Measurements of the transient photoconductivity using transit time techniques have been carried out on pure rutile single crystals in the temperature range 300 K to about 40 K. The induced charge signals observed do not indicate a well defined break point at the transit time but are composed of the initial fast response and the subsequent slow response. From the temperature dependence of the time constant of the slow response, two trap levels with different energy depth for electrons and holes, respectively, are found in the measured temperature range. The energy depth of one of the trap levels for holes depends on the electric field and is explained by the simple Poole-Frenkel effect. The temperature dependence of the magnitude of fast response shows that the conduction for both electrons and holes is the band type conduction and the scattering is dominantly affected by the optical lattice vibrations. The results for the transport of hole carriers are first obtained in this study.