DC electric and photoelectric measurements of CdTe thin films in Schottky-barrier cells

Abstract

Measurements of the temperature dependence of ohmic and space-charge-limited (SCL) currents on thin films of polycrystalline particles of cadmium telluride in Schottky-junction cells have been carried out in air ambient. These cells showed rectification where p-CdTe material was flanked between an ohmic contact (Au) and a blocking contact (Al). At low voltages, the dark current in the forward direction which corresponds to negative potential at the Al electrode varies exponentially with voltage. At higher voltages, two distinct regions of ohmic and SCL conduction limited by a discrete trapping level are determined. Traps with a density of 3.85×10 22 m −3 located at 0.58 eV above the valence band edge have been observed. The thickness dependence in the square-law region has been found to confirm the d −3 law. Values of conversion efficiency as high as 11.3% and open-circuit voltage of 0.77 V have been evaluated from the photo-measurements of J– V characteristic at input power density of 100 mW cm −2. Space-charge concentrations and barrier heights have been estimated from the capacitance–voltage ( C– V) measurements both in dark and under constant illumination. The linearity of the C −2– V dependence is associated with a homogenous distribution of the impurities inside the space-charge region.