A model for low temperature interface passivation between amorphous and crystalline silicon

Abstract

Excellent passivation of the crystalline surface is known to occur following post-deposition thermal annealing of intrinsic hydrogenated amorphous silicon thin-film layers deposited by plasma-enhanced chemical vapour deposition. The hydrogen primarily responsible for passivating dangling bonds at the crystalline silicon surface has often been singularly linked to a bulk diffusion mechanism within the thin-film layer. In this work, the origins and the mechanism by which hydrogen passivation occurs are more accurately identified by way of an interface-diffusion model, which operates independent of the a-Si:H bulk. This first-principles approach achieved good agreement with experimental results, describing a linear relationship between the average diffusion lengths and anneals temperature. Similarly, the time hydrogen spends between shallow-trap states is shown to decrease rapidly with increases in temperature circuitously related to probabilistic displacement distances. The interface reconfiguration model proposed in this work demonstrates the importance of interface states and identifies the misconception surrounding hydrogen passivation of the c-Si surface.