PHOTOCONDUCTIVITY AND DARK-CONDUCTIVITY STUDIES OF TIO2-ZNO SOLID-SOLUTIONS

The present paper deals with the photoconductivity and dark-conductivity measurements of TiO2-ZnO solid solution. The photocurrent takes a long time to saturate for 60% TiO2-40% ZnO system as soon as the light is switched on. However, for 20% TiO2-80% ZnO and 100% TiO2 Systems, the photocurrent reaches saturation values quickly. For 100% TiO2 sample, the dark current is found to be trap-limited space-charge-limited, while it shows nonohmic behaviour for 20% TiO2-80% ZnO system at higher voltages. The photocurrent tends to saturation at higher voltages for both systems. The nature of photocurrent versus intensity curve changes from superlinearity to sublinearity. This confirms the presence of sensitizing centres near the valence band and the existence of an exponential trap distribution near the conduction band. The decrease in current with temperature can also be explained on the basis of these sensitizing centres. The X-ray diffraction patterns of the samples with different compositions show the formation of solid solutions. SEM (scanning electron microscopy) of the 20% TiO2-80% ZnO system shows the surface structure of the material.