Electronic effects of ion mobility in semiconductors: Semionic behaviour of CuInSe₂

Application of strong electric fields at ambient temperatures to crystals of CuInSe₂ and (Cu,Ag)InSe₂ semiconductors can create non-equilibrium doping profiles, stable after removal of the electric field, as illustrated by formation of μm-sized single and multiple diode structures in initially homogeneous and uniformly doped single crystals. Phototransistor action and amplification was obtained, clear evidence for the presence of junctions, resulting from non-equilibrium doping profiles. Electron beam-induced current measurements, combined with current-voltage, capacitance-voltage and time-dependent current measurements, as well as numerical simulations were performed to characterize and understand the phenomena. Control experiments exclude formation of extended defects or the occurrence of contact diffusion. Localized Joule heating that occurs around the contact cannot by itself account for the observed phenomena. Because these chalcopyrites contain relatively mobile components [Cu,Ag], which are also dopants, we interpret these observations as a result of internal dopant redistribution, aided by localized temperature increases and directed by the electric field.