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

We investigate the mechanism for Si dangling bond defect creation in amorph ous 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 o r 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 locali zed 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 involvi ng the long-range diffusion of hydrogen. Our experimental results demonstra te the importance of optimizing the intrinsic stress in the films to obtain maximum stability and mobility. An important implication is that a deposit ion process where intrinsic stress can be independently controlled, such as an ion-energy controlled deposition should be beneficial, particularly for deposition temperatures below 300 degrees C. (C) 2000 American Institute o f Physics. [S0021-8979(00)10001-5].