Improvement in the optical absorption of PECVD microcrystalline Si thin film through modification of the crystalline fraction through an annealing process

Abstract

Intrinsic microcrystalline silicon (μc-Si) thin films with varying crystalline fractions ( X C) were deposited using plasma-enhanced chemical vapor deposition. Effort was made to modify the X C and optical properties by annealing at different temperatures, pressures, and ambient gases. After annealing, the amount of Si–H in the μc-Si thin film was decreased for an initial X C of 7%, while that of Si–H 2 mainly decreased to an initial X C of 60–70%. The X C of μc-Si with an initial X C of 7% increased by annealing. However, initial X C of 60% and 70% resulted in a decrease of X C upon annealing. It is suggested that an increase in crystal size of μc-Si films by annealing decreases X C, while a decrease in crystal size increases X C. Depending on the annealing conditions, the optical absorption property of the μc-Si thin film changed. When the initial X C was 7%, the absorption coefficient increased as X C increased to 16%, but slightly decreased with X C values from 51% to 70%. Therefore, we suggest that there is an optimum X C that exhibits the highest optical absorption.