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The threshold voltage (Vth) shift of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) have been investigated for the atmospheric pressure chemical vapor deposition (APCVD) silicon dioxide (SiO2) gate insulator. For both positive and negative gate bias stress, the threshold voltage was shifted in the positive direction and was dominated by the defect creation near the a-Si:H/SiO2 interface. There was little charge trapping into the APCVD SiO2 gate insulator under the gate bias stress. For the positive gate bias stress, the threshold voltage shifts of a-Si:H TFTs with the a-Si:H/SiO2 interface were smaller than those of the conventional a-Si:H TFTs with the a-Si:H/SiNx interface.

Light-induced changes in vibrational absorption of SiHn have been studied for a-Si:H films. The stretching mode absorption near 2000 cm−1 decreases after light exposure. The magnitude of the change increases as the substrate temperature is lowered, and little change is observed for a-Si:H films deposited above 200°C. From the changes both for the peak and the spectrum, it is suggested that the hydrogen in the bulk diffuses to the microvoids, where it can combine to form H2 in low substrate temperature sample. The B-H modes increase after light soaking, Which is related with the increase in doping efficiency of boron, which is confirmed from the conductivity change with time during illumination.