The effect of high concentration of phosphorus in aluminum-induced crystallization of amorphous silicon films

Abstract

Polycrystalline silicon (poly-Si) film prepared by aluminum-induced crystallization (AIC) of highly phosphorus (P)-doped amorphous silicon has been proposed for suppressing Si islands and voids. Si islands on the poly-Si surface and voids at the interface between the poly-Si and the glass are caused by Si atoms' out-diffusion toward the top surface during the AIC process, which also degrades the electrical characteristics of the film. High-P dopants can form P precipitations and retard the out-diffusion of Si atoms, hence suppressing Si islands and voids. Also, P precipitations can enhance the crystallization rate and grain growth. P dopants act as donors and compensate for the p-type poly-Si film, which is formed by Al doping during the AIC process. The hole concentration of undoped poly-Si is reduced by approximately three orders to 7×1012cm−3. Such near-neutral poly-Si films could be applied as intrinsic (i) layers in p-i-n structures to explore solar cell applications. Also, the enhanced quality of P-doped AIC-Si increases the mobility by five times owing to reduced scattering and trap density.