Mechanism of charge transfer in n-CdS/p-CdTe heterojunctions

The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe1−xSx solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10−8-10−5 A cm−2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10−4-10−2 A cm−2 is limited by recombination of charge carriers in the electroneutral region of the CdTe1−xSx solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe1−xSx solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe1−xSx solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe1−xSx is an i layer, and CdS is an n layer.