The interface effect on the I–V curves and analysis of ionic diffusion coefficients of polycrystalline CuIn4Te6

A polycrystalline CuIn4Te6 slice is a mixed ionic and electronic conductor. Under application of a constant voltage, Vm, to the sample, complex variations of the current intensity as a function of time have been observed due to the motion of two ions. Several I–Vm relations and hysteresis effects have been fully explained for different applied voltage ranges and measuring times. The complex variations of I with time can be only understood taking into account dynamic processes of arrival and departure of two mobile ions, Cu and In, at the semiconductor/electrode interface. An equivalent electrical circuit has allowed computing the voltage drop at the semiconductor/electrode interface, Vc, and the electronic current, I1, produced by potential changes at the interface region induced by the ionic motion. Likewise, striking hysteresis effects in I1–Vm and Vc–Vm relations have been observed. The existence of a residual voltage at the interface due to ionic accumulation from previous measurements has to be taken into account to fully explain the hysteresis cycles, where the difference between the applied external voltage and the residual voltage at the interface is the key parameter controlling the complex charging or discharging processes taking place at the semiconductor/electrode interface. The existence of such remaining interface potential is supported by the asymmetric Cu enrichment observed in the compositional profile obtained by energy dispersive X-ray spectroscopy along the sample thickness. Two different ionic diffusion coefficients have been computed from the evolution of conductivity as a function of the inverse of time, but it is not straightforward to decide which coefficient is associated with Cu or In.