Electrical conductivity and the effect of temperature on photoconduction of n-ZnSe/p-Si rectifying heterojunction cells

Electrical and photoelectrical measurements are made at different temperatures on heterojunction photovoltaic cells fabricated by vacuum deposition of n-ZnSe thin films onto p-Si single crystals. A complete study of the current as a function of voltage and temperature is carried out in order to gain fundamental information on trap depth, trap distribution and position of the Fermi level. The results are consistent with space-charge-limited conduction due to an exponentially decreasing distribution of traps. At low voltages, the dark current in the forward direction varies exponentially with voltage. Under reverse bias, the conduction process is interpreted in terms of a transition from electrode-limited Schottky emission to the bulk-limited Poole-Frenkel effect, The values of thermal activation energy for photoconduction and effective density of conducting states are determined and found to be 0.22 eV and 4.4 x 10(17) cm(-3), respectively. These values are estimated from the dependence of photocurrent on temperature at constant illumination with an input power density of 50 mW cm(-2).