Dispersive electron transport in polycrystalline films of CdTe

Electron transient transport has been studied in CdTe polycrystallilne films by means of the time-of-flight technique. The samples studied were intrinsic CdTe polycrystalline films with a grain size from about 100 nm to 20 {μ}m. The transit time was measured in the largest-grain-size films. The transient transport has the characteristics of dispersive transient transport as observed in disordered materials such as amorphous semiconductors, glasses, etc. For the smaller-grain-size films it is not possible to determine a transit time in the photocurrent traces, due to the effects of recombination and deep trapping of charge. However, the transport characterization allows the determination of the dispersive nature of the electron transport in these films. In addition, in one kind of these smaller-grain-size films, it was possible to identify the presence of a localized state as being responsible for the photocurrent peak exhibited in the photocurrent traces. This peak is explained by a multiple-trapping model with a single-trapping level along with a recombination center.