通过光电子产额光谱法研究了非晶硅(a-Si:H)在高于带隙光照射下缺陷态密度的瞬态变化。532nm激光以50mW/cm²的激发密度调制，频率范围0.1Hz至10kHz，观察到光电子产额信号的瞬态响应。结果显示在费米能级下方约0.3eV处缺陷态密度增加，最大增加量约为10^17cm³/eV，而在EF-0.75eV的深尾态区则减少。研究表明，这种状态的再分布并非由光照引起的表面带边弯曲变化或电子从占据态到空态的简单激发引起，而是弱键转换为悬挂键的过程，即Staebler-Wronski效应的前驱，但缺乏氢稳定化的最后步骤以形成亚稳态缺陷。
摘要：
Photoelectron Yield Spectroscopy is one of the most direct methods to study the density of gap states of amorphous semiconductors. We have made use of it to investigate the transient changes of the density of gap states of a-Si:H upon illumination with above-band-gap light. An excitation density of 50 mW/cm2of 532 nm light from a frequency doubled Nd-YAG laser was modulated with frequencies between 0.1 Hz and 10 KHz and the transient response of the photoelectron yield signal was monitored by gated electron counting or a lock-in amplifier. From this we deduce a reversible increase of the occupied density of defect states under illumination with a maximum Δg ∼ 1017 cm3eV-1at about 0.3 eV below the Fermi energy and a decrease below EF− 0.75 eV, i. e. in the region of deep tail states. The effect exhibits a wide spectrum of time constants involved. Based on additional transient surface photo voltage measurements as well as numerical simulations we argue that the observed redistribution of states is not due to a light induced change in surface band bending or due to a mere excitation of electrons from occupied to empty states. Instead, we interpret the observed effect as a conversion of weak to dangling bonds, i.e. a precursor of the Staebler-Wronski Effect, lacking however the final step of hydrogen stabilisation necessary for the creation of metastable defects.
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