Abstract
Using detailed computer simulations we explore the origin of the current density differences experimentally observed in the dark current density—voltage (J—V) characteristics of hydrogenated amorphous Si (a-Si:H) Schottky barriers and a-Si:H p—i—n homojunctions. Schottky barrier devices show higher dark current densities at low forward biases and p—i—n devices show higher current densities at high forward biases. Computer modelling shows that at low forward voltages the transport mechanism limiting the total current density is drift diffusion over the barrier in Schottky barriers and recombination through localized states in p—i—n diodes. On the other hand at high forward bias voltages the limiting transport mechanism is electron space-charge-limited current in both devices. We found that the non-blocking nature of the p—i—n front contact is the ultimate cause for the higher current densities observed experimentally in a-Si:H p—i—n structures at high forward biases. In this paper we also compare the illuminated forward-bias J—V characteristics of both devices when they are forward biased past the flat-band condition and we show fits to experimental results for both dark and illuminated forward-bias J—V characteristics for devices with two different thicknesses of the intrinsic layers.
