Defect pool modelbased transient photoconductivity and the conduction band tailprofile in a-Si:H

Abstract

The energy profile of the density of states (DOS) over themobility gap is determined jointly by the defect pool model(DPM) calculation and the Fourier transform of the transientphotoconductivity (TPC), for intrinsic and phosphorus(P)-doped a-Si:H. From the Fourier transform of the TPC, we measure, as a doping effect, an increase of the DOS around thedonor energy level, at about 0.16 eV below the conductionmobility edge, and a decrease of the tail width below thislevel from 21 to 15 meV. This disorder effect on the conductionband tail caused by the P dopant is consistent with the induceddoping changes in the dangling bond defect distributioncalculated by the DPM. TPC decays are then generated bynumerical simulation using this DOS distribution and comparedto experimental TPC data. All observed features in thetransient photoresponse are reproduced by the simulation, namely the short time rapid decrease followed by the long powerlaw decay in the intrinsic a-Si:H, and the long non-dispersiveflat region in the P-doped a-Si:H.