Tuning optical and electrical properties of zinc oxide PLD films: effect of temperature and air annealing

The effect of substrate temperature and post-deposition thermal annealing on the optical and electrical properties of ZnO thin films grown by pulsed laser deposition are studied. XRD analysis reveals a (002) orientation and stress relaxation with increasing growth temperature. AFM shows a granular surface topography, whose grains become larger after annealing. Competition of coalescence and recrystallisation mechanisms is proposed to explain these results. Optical transmission experiments reveal changes in the relative intensity of the defect bands in the visible region, caused by changes in the population of intrinsic defects. Electrical measurements find that room-temperature grown films are p-type, while higher-temperature deposited films are n-type, and all become p-type after annealing. Low-temperature measurements reveal a switch in the conductivity type from p- to n-type around 220-250 K depending on the samples, which is explained due to competing defect-related conduction mechanisms.