Defect Relaxation in a-Si:H Studied by Defect Absorption and Luminescence

Abstract

The experimental results about defect relaxation in a-Si:H have been reported recently on several transient measurements, such as forward-bias-transient-current,1 optical bias effect on electron drift,2 and photo-capacitance transient.3 In this paper we report the steady state results of the bias effect on sub-band-gap absorption and photon-emission spectra measurements in undoped samples.The optical bias effects the sub-band absorption. In additional to an enhancement of the sub-band gap absorption, the absorption threshold moved from 0.8 eV to 0.6 eV for undoped samples under optical bias at room temperature. The effects are larger in the light-soaked-state than in the annealed-state.We also report on the generation rate dependence on photoluminescence (PL) spectra line shape. We found that the energy position of the defect PL band shifted from 1.1 eV to 0.9 eV when the excitation level increased 4,000 times.While motion of the quasi-Fermi level as a explanation cannot be eliminated, defect relaxation seems more plausible.