A possible mechanism for the behaviour of a p–n, II–IV amorphous heterojunction

A phenomenological model is suggested for an amorphous p–n heterojunction. The forward bias currents are influenced by the large mobility decrease that occurs for majority carriers in extended states as they arrive at the junction region and enter hopping states. A zero-bias barrier exists but this increases with forward bias since the mobility mismatch initially produces a change in the space charge region width as well as a decrease in the average space charge density with increasing current density. At larger forward biases, the space charge region width tends to saturate and the average space charge density begins to increase.The reverse bias breakdown current is due to majority carrier tunneling. This model developed from the observed I–V characteristics is used to predict results that are compared with the measured current-temperature (at fixed bias) and bias-capacitance variations for actual devices.