Defect pool model based transient photoconductivity and the conduction band tail profile in a-Si:H

The energy profile of the density of states (DOS) over the mobility gap is determined jointly by the defect pool model (DPM) calculation and the Fourier transform of the transient photoconductivity (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 the donor energy level, at about 0.16 eV below the conduction mobility edge, and a decrease of the tail width below this level from 21 to 15 meV. This disorder effect on the conduction band tail caused by the P dopant is consistent with the induced doping changes in the dangling bond defect distribution calculated by the DPM. TPC decays are then generated by numerical simulation using this DOS distribution and compared to experimental TPC data. All observed features in the transient photoresponse are reproduced by the simulation, namely the short time rapid decrease followed by the long power law decay in the intrinsic a-Si:H, and the long non-dispersive flat region in the P-doped a-Si:H.