Relative importance of the Si–Si bond and Si–H bond for the stability of amorphous silicon thin film transistors

Abstract

We investigate the mechanism for Si dangling bond defect creation in amorphous silicon thin film transistors as a result of bias stress. We show that the rate of defect creation does not depend on the total hydrogen content or the type of hydrogen bonding in the amorphous silicon. However, the rate of defect creation does show a clear correlation with the Urbach energy and the intrinsic stress in the film. These important results support a localized model for defect creation, i.e., where a Si–Si bond breaks and a nearby H atom switches to stabilize the broken bond, as opposed to models involving the long-range diffusion of hydrogen. Our experimental results demonstrate the importance of optimizing the intrinsic stress in the films to obtain maximum stability and mobility. An important implication is that a deposition process where intrinsic stress can be independently controlled, such as an ion-energy controlled deposition should be beneficial, particularly for deposition temperatures below 300 °C.