Spatial and Temporal Variations in Electronic Transport Through a CdTe-Based Schottky Barrier

We study the electric current through metal-semiconductor junctions of a type used in thin-film PV for back contacts. To concentrate on one type of junction we used the symmetric structures of rf-sputtered CdTe layer sandwiched between two Cr contacts. Along with the conventional measurements, the current-sensing contact mode AFM was employed to measure the current-voltage characteristics and current variations with time under fixed voltage. We found that (i) the electric current flow is laterally strongly nonuniform; (ii) it chaotically varies over time; (iii) this behavior did not correlate with surface topography. We interpret our observations in terms of defect assisted tunneling through time-dependent defect pathways.