New Evidence for Deep Defect Relaxation in Hydrogenated Amorphous Silicon from Junction Capacitance Methods

Abstract

AbstractWe have carried out capacitance transient measurements on lightly PH3 doped a-Si:H films incorporating both ohmic and blocking contacts. We find that the previously reported anomalous variation of emission time with filling pulse duration is completely independent of whether one uses an n+ c-Si substrate (providing a reasonably ohmic back contact) or a p+ c-Si substrate (giving a blocking back contact). Quite similar behavior is observed on a sample which includes an n+ a-Si:H layer at the back contact, exhibiting a variation of more than 2 orders of magnitude change in emission time when the filling pulse duration is decreased from Is to 100μs. Computer simulations are used to demonstrate that for a fixed (non-relaxing) deep state distribution, a filling problem in general cannot account for the observed experimental behavior. Finally, we report measurements that demonstrate that the filling of defects too close to the barrier interface can create difficulties observing the relaxation effects when an n+ a-Si:H contacting layer is used.