ON THE NATURE OF PHOTOCURRENTS IN K1-XLIXTAO3

We have undertaken photo-Hall effect and photocurrent kinetics measure ments in K0.984Li0.016TaO3 and K0.966Li0.034TaO3 single crystals, unde r irradiation with photons of energy lower than the band gap. Photocur rents are carried by electrons, whose mobility is little dependent on temperature. The strong enhancement of photocurrent observed in the po lar phase is therefore to be ascribed to a corresponding increase in c arrier density. Poling conditions also affect low temperature current levels. A new feature is the observation of persistent currents after shut-off of illumination. The present results strongly support the imp ortance of hole traps with vanishing cross section for electron recomb ination and point out the role of the dipole-glass transition.