Thermal equilibrium, the Staebler-Wronski effect and potential fluctuations in lithium-doped hydrogenated amorphous silicon

We report the effect of fast thermal quenching (FQ) and light soaking (LS) on electronic transport in lithium-doped hydrogenated amorphous silicon (a-Si:H(Li)), and compare the two instabilities in the same specimen. We find that the metastable changes are qualitatively similar to those in phosphorus-doped hydrogenated amorphous silicon. The films are in thermal equilibrium above the temperature T E, which is lower for heavier doping. However, for a given sample, the TE values are about the same for FQ and LS. Isothermal relaxation of conductivity [sgrave] of the metastable states follows a stretched exponential, but the relaxation parameters for FQ and LS are different. We also find that the function Q = In [sgrave] - eS/k shows a large change after LS but hardly changes after FQ. The results are explained by assuming that the recombination of carriers at the local minima of the potential fluctuations present on a-Si: H(Li) gives rise to structural changes. The observed increase in the slope of Q versus 1/T after LS is interpreted as an increase in potential fluctuations. The very smali change in Q observed after FQ is explained in terms of the higher mobility of hydrogen at the high temperature from which a-Si: H is quenched.