Conduction behavior conversion for Cu-doped ZnS/n-type Si devices with different Cu contents

Currents through Cu-doped ZnS (ZnCuS)/n-type Si structures were studied. The electrical conduction investigations suggest that the carrier transport behavior is governed by the Poole–Frenkel emission for ZnCuS/n-type Si devices having the low Cu concentration. However, the carrier transport behavior is governed by the thermionic emission for ZnCuS/n-type Si devices having the high Cu concentration. The photoluminescence result revealed that sulfur vacancy (V_S) is the origin of conduction behavior conversion. It is shown that the increased Cu concentration leads to the reduced formation probability of V_S. The dependence of V_S on the film composition was identified for providing a guide to control the current transport behavior of ZnCuS/n-type Si devices.