Investigation of deep levels in PbI2 by photoinduced current transient spectroscopy

Abstract

Deep levels in PbI₂ have been investigated by photoinduced current transient spectroscopy for the first time. By separating the signal processing from the data acquisition it was possible to analyze the transient using different methods, in particular a four‐gate treatment which allows to clear the detrapping current of uncontrolled changes of the recombination lifetime of thermally released carriers. Three hole traps located at 0.30, 0.47, and 0.66 eV have been detected and the corresponding thermal capture cross sections evaluated. In addition a photomemory effect has been evidenced. The main features of the excited state of the crystal are increased photosensitivity, neutralization of hole traps, and residual conductivity. It is believed that macroscopic recombination barriers acting as minority carrier traps under optical excitation are responsible for this phenomenon. The presence of these extended defects is probably related to the layered structure of PbI₂. An energy model is proposed on the basis of which the observed logarithmic time dependence of the photosensitization at room temperature can be predicted. The model allows also to give a plausible interpretation for all the characteristic features of the photomemory effect and for various results previously reported by other authors.