Numerical Modelling of Time-of-Flight in SCLC-Mode

Abstract

ABSTRACTThe application of time-of-flight (TOF) in the space charge limited current (SCLC) mode to a-Si:H pin-diodes has led to the discovery of new features in the current transients. An alternative to analytic models, our numerical modelling describes the specific nature of amorphous semiconductors by taking into account the interaction of free carriers with tail states and the contribution of trapped carriers to the space charge. Typical features of experimental SCLC-TOF-currents such as a cusp in the transient can be reproduced. We confirm the concept of ‘effective thickness’ for the determination of the transit time. At high injection intensity only a small fraction of the charge can be collected. Bimolecular recombination via tail states and surface recombination is identified as a loss mechanism that competes with recombination via dangling bonds. The post-transit behaviour of electron-TOF is dominated by holes emitted from the valence band (vb) -tail. The density of states distribution from post-transit-spectroscopy (PTS) shows features of the vb-tail. Finally, hole SCLC-TOF shows a different behaviour from electron SCLC-TOF.