OPTICAL-BIAS EFFECTS IN ELECTRON-DRIFT MEASUREMENTS AND DEFECT RELAXATION IN A-SIH

We report measurements of the effects of optical bias upon photocharge transients in a-Si:H. Transients were recorded from 100 ns to 10 s fo llowing a laser pulse. Without optical bias these transients exhibit a form consistent with trapping of electrons by a deep level; this resu lt is consistent with extensive prior research. However, even low leve ls of optical bias (generation rate 10(17) cm-3 s-1) suppress deep tra pping, leading to an enhancement of electron drift by as much as one d ecade. We propose that charge state transitions associated with optica l bias leave defects in metastable configurations. The corresponding t ransition energies lie closer to the conduction band than for the defe ct's relaxed, equilibrium configuration.