Mechanism of charge transfer in $n$-CdS/$p$-CdTe heterostructures with a thick layer of the CdTe$_{1-x}$S$_x$) solid solution

The current-voltage and capacitance-voltage characteristics of the $n$-CdS/$p$-CdTe heterosystem are investigated. An analysis of the results obtained has demonstrated that a high-resistance $i$ layer (the CdTe$_{1-x}$S$_x$) solid solution), which is inhomogeneous not only in the electrical conductivity but also in the composition, is formed at the $n$-CdS/$p$-CdTe heterointerface. The thicknesses of the solid-solution layers are estimated from the capacitance-voltage characteristics, and regions with different types of conduction are found to exist in the intermediate layer. It is shown that the ambipolar diffusion and drift in the high-resistance CdTe$_{1-x}$S$_x$) solid-solution layers are directed toward each other, thus resulting in the appearance of a sublinear portion in the current-voltage characteristics described by the dependence $V = \exp(Iaw)$. The observation of a sublinear portion in the current-voltage characteristics measured in both the forward and reverse electric current directions over a wide temperature range 77–323 K suggests that the diffusion-drift regime can occur in different parts of the $i$ layer, depending on the electric current density and the ambient temperature. The changes observed in the electric current and capacitance, as well as in the current-voltage and capacitance-voltage characteristics, after ultrasonic irradiation indicate that, in the CdTe$_{1-x}$S$_x$) solid solutions, there exist metastable states, which most probably decay under ultrasonic irradiation and then again form solid solutions with more stable states.