Structural change and photo-response in porous poly-Si/Si

Abstract

We performed scanning electron microscopy (SEM), dark and photo-conductivities, and the persistent photo-conductivity effect for porous poly-Si/Si. SEM images showed that the electrochemical anodic process not only changed the surface of polycrystalline silicon film but also the interface between the polycrystalline silicon film and substrate. In fact, as the electrochemical anodisation proceeded, columns connected by grain boundaries in the poly-Si film turned to channels of anodisation current, and the surface and interface transformed to the porous surface. Current-voltage curves for the structures with varied porous surface and interface, indicated that the structure with a large porous area yielded a rectification curve combined with an ohmic behaviour due to the increased series resistance. The study on the persistent photo-conductivity effect resulted in the logarithmic time decay. The logarithmic time dependence may be explained by the charge separation model. Trapping centres formed in the energy band gap capture photo-generated holes and prohibit the holes from recombining with electrons due to the potential barrier produced by the porous interface. (C) 2000 Elsevier Science S.A. All rights reserved.