Thin-film transistors (TFTs) with different silicon nitride (SiNx) gate compositions and various hydrogen concentrations in their amorphous silicon films (a-Si:H) have been stressed with positive and negative biases to realize the instability mechanisms. For both stress polarities, it is found that the threshold voltage shifts significantly increase due to the trap sites in the SiNx gate. As the effects of the trapped charges in the SiNx films are reduced, the anomalous threshold voltage shifts under negative stress voltage are observed. The creation of the states near the conduction band in the a-Si:H films can be enhanced according to the defect pool concept and stimulated by the hydrogen contents in the a-Si:H films, which can be confirmed by the subthreshold swing change. Therefore, the negative threshold voltage shifts caused by the hole trapping in the SiNx gate are positively compensated by the created states, reflecting the turnaround behaviors for the threshold voltage shifts. As for the positive stress, the state creation in the a-Si:H films can be suppressed via the defect pool mechanism and thus the threshold voltage shifts are dominantly affected by the electron trapping in the SiNx gates.

Decays from highly ionized fluorine atoms obtained by beam-foil techniques are examined in the 670 eV to 1150 eV range. Transitions from the one-electron, two-electron and three-electron configurations are observed. In the H-like and He-like spectra the lines agree well with the known values, and the series limits were observed. The observed Lilike lines are compared with existing calculations and measurements. Two lines, at 800.6 eV and 813.2 eV, are observed but no good agreement is found with any existing calculations.

Carrier-induced changes in the gap states of plasma-enhanced-chemical-vapor-deposited (PECVD) undoped a-Si:H films are systematically studied using isothermal capacitance transient spectroscopy (ICTS) method via the novel structure we proposed previously. The density-of-state distribution g (E) and the energy dependence of electron-capture cross section σn (E) of gap states in undoped a-Si:H films before and after injection of electrons are directly measured for the first time. Experimental results show that the density of g (E) increases but the σn (E) has no obvious change after the electron injection. These indicate that the defects created during the electron injection are the same in type as those of the as-deposited films. In addition, it is found the shape of g (E) distorts after the injection, implying that the gap states with different energy levels are associated with distinct types of defects.