Photoinduced electronic transport in ${\mathrm{K}}_{1-x}{\mathrm{Li}}_x{\mathrm{TaO}}_3$

Photocurrent and Hall effect measurements were performed on ${\mathrm{K}}_{0.984}{\mathrm{Li}}_{0.016}{\mathrm{TaO}}_3$ and ${\mathrm{K}}_{0.966}{\mathrm{Li}}_{0.034}{\mathrm{TaO}}_3$ single crystals under illumination with 514.5-nm and UV light. The currents observed are carried by electrons, whose mobility does not undergo large variations on cooling across the dipole-glass freezing temperature $T_f.$ The sharp increase of photocurrent occurring in the polar phase is primarily due to enhancement of carrier density. The effect is much larger after field cooling, being accompanied in this case by persistent currents. The present results lead us to conclude that hole traps with vanishing cross section for electron recombination are active below $T_f.$