Bandgap enhancement of layered nanocrystalline silicon from excimer laser crystallization

Abstract

Excimer laser irradiation is used to crystallize hydrogenated amorphous silicon thin films.The resulting films show a stratified microstructure with a crystalline volume fraction ofup to 90%. There is a range of excimer laser energy that can produce stratifiednanocrystalline silicon with a Tauc gap as high as 2.2 eV. This value is greater than thatof amorphous or crystalline silicon and is contrary to that predicted from thetheoretical analysis of mixed-phase silicon thin films. The phenomenon is explainedby employing transmission electron microscopy and spectroscopic ellipsometry,and the observed bandgap enhancement is associated with quantum confinementeffects within the nanocrystalline silicon layers, rather than an impurity variation.