The band gap in silicon nanocrystallites

Abstract

The gap in semiconductor nanocrystallites has been extensively studied boththeoretically and experimentally over the last two decades. We have compared arecent ‘state-of-the-art’ theoretical calculation with a recent ‘state-of-the-art’experimental observation of the gap in Si nanocrystallite. We find that the two arein substantial disagreement, with the disagreement being more pronounced atsmaller sizes. Theoretical calculations appear to overestimate the gap.To reconcile the two we present two scenarios. (i) Recognizing that theexperimental observations are for a distribution of crystallite sizes, we proffer aphenomenological model to reconcile the theory with the experiment. We suggestthat similar considerations must dictate comparisons between the theoryand experiment vis-à-vis other properties such as radiative rate, decayconstant, and absorption coefficient. (ii) Either surface passivation orsurface orientation may also resolve the conflict between the theory and theexperiment. We have carried out tight-binding calculations on siliconclusters to study the role of surface passivation and surface orientation.