Impedance Spectroscopy and Hall Measurements on CdTe Thin Polycrystalline Films

Measurements of film impedance in a wide frequency range (impedance spectroscopy, IS) were used to evaluate the grain boundary (GB) and the bulk material (B) resistance. Undoped films demonstrated very low carrier concentration and negligible GB resistance, both due to depletion of the bulk material by the GB deep states. Doping the film with Cu led to a significant increase in the GB resistance, in addition to the expected increase in carrier concentration. Illumination of doped films reduced GB resistance by orders of magnitude. This effect was used for the analysis of Hall concentration and Hall mobility data, aimed at exclusion of GB influence on measured parameters, and was used to determine the carrier concentration and mobility in the grain bulk. Hall studies on undoped films under illumination were also used to estimate the lifetime of the photogenerated carriers.