Numerical simulation of the transient photoconductivity in a-Si:H as a function of the excitation density

摘要

The dependence of the transient photoconductivity induced by pulsed excitation (TPC) on the excitation desity is discussed with the help of numerical simulations.It is shown that recombination between excess mobile electrons and all excess holes (mainly localized) can explain the excitation density dependence o fthe TPC amplitude of standard a-Si:H at room temperature using a rate parameter K_BB of 10~-8 cm~3/s. This model leads to a decay faster than experimentally observed in the time range from 40 ns to 1 um s.A variation of the recombination model is presented that gives a better fit for the longer time range still showing the correct excitation density dependence in the short time range.Morecover comparison of the simulations with experimental data yields limits for the paameters of the conduction band tail.In particular,the time necessary to establish a dynamic equilibrium of excessw electrons between delocalized states in the conduction band and localized states in the tail appears to be very informative.