Evolution of an amorphous silicon network from silicon paracrystallites studied by spectroscopic ellipsometry

Abstract

A common concept is that crystalline silicon ($c\text{\ensuremath{-}}\text{Si}$) has short-range order (SRO) and long-range order (LRO), while amorphous silicon has only SRO consistent with the continuous random network model. Spectroscopic ellipsometry measurements show that in the initial stage of growth, ultrathin $a\text{\ensuremath{-}}\text{Si}:\mathrm{H}$ films deposited by thermal chemical-vapor deposition at $460\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ contains deformed crystallites or paracrystallites. Paracrystallites have SRO and medium-range order (MRO). Hence the ultrathin $(4--10\phantom{\rule{0.3em}{0ex}}\text{nm})\phantom{\rule{0.3em}{0ex}}a\text{\ensuremath{-}}\text{Si}:\mathrm{H}$ network possesses MRO with SRO. During the growth, paracrystallites gradually change into a continuous random network.