Dangling-bond defect state creation in microcrystalline silicon thin-film transistors

We analyze the threshold voltage shift in microcrystalline Si thin-film transistors (TFTs), in terms of a recently developed thermalization energy concept for dangling-bond defect state creation in amorphous Si TFTs. The rate of the threshold voltage shift in microcrystalline Si TFTs is much lower than in amorphous Si TFTs, but the characteristic energy for the process, which we identify as the mean energy to break a Si-Si bond, is virtually the same. This suggests that the same basic Si-Si bond breaking process is responsible for the threshold voltage shift in both cases. The lower magnitude in microcrystalline Si TFTs is due to a much lower attempt frequency for the process. We interpret the attempt frequency in amorphous and microcrystalline silicon in terms of the localization length of the electron wave function and the effect of stabilizing H atoms being located only at grain boundaries.