Characterization of defect removal in hydrogenated and deuterated amorphous silicon thin film transistors

Abstract

Thin film transistors (TFTs) utilizing an hydrogenated amorphous silicon (a-Si:H) channel layer exhibit a shift in the threshold voltage with time under the application of a gate bias voltage due to the creation of metastable defects. These defects are removed by annealing the device with zero gate bias applied. The defect removal process can be characterized by a thermalization energy which is, in turn, dependent upon an attempt-to-escape frequency for defect removal. The threshold voltage of both hydrogenated and deuterated amorphous silicon (a-Si:D) TFTs has been measured as a function of annealing time and temperature. Using a molecular dynamics simulation of hydrogen and deuterium in a silicon network in the H2∗ configuration, it is shown that the experimental results are consistent with an attempt-to-escape frequency of (4.4±0.3)×1013Hz and (5.7±0.3)×1013Hz for a-Si:H and a-Si:D respectively which is attributed to the oscillation of the Si–H and Si–D bonds. Using this approach, it becomes possible to describe defect removal in hydrogenated and deuterated material by the thermalization energies of (1.552±0.003)eV and (1.559±0.003)eV respectively. This correlates with the energy per atom of the Si–H and Si–D bonds.