Gas phase synthesis and processing of silicon nanocrystallites: Characterization by photoluminescence emission spectroscopy

Abstract

A nonequilibrium vapor-phase approach to the synthesis and processing of semiconductor nanoparticles is applied to the deposition of self-supporting thin films of agglomerated Si nanocrystallites. Silicon nanocrystallites are created using a laser ablation supersonic expansion source. Average particle size is controlled through variation of process parameters, including relative ablation pulse/gas valve timing and nozzle length. As-deposited thin films of agglomerated Si nanocrystallites are passivated via a hydrofluoric acid (HF) etch/roomtemperature oxide growth process and then characterized using room-temperature photoluminescence (PL) emission spectroscopy. Clear spectral trends are seen in the PL emission data, which correlate with changes in mean particle size as controlled through process parameter variation or repeated HF etch/oxide regrowth cycles. Photoluminescence emission studies of gas-phase, isolated Si nanocrystallites reveal no visible emission. We conclude that quantum size effects play a necessary but not sufficient role in enabling the PL emission behavior of nanocrystalline Si. Passivation of the Si nanocrystallite surfaces is also necessary to kinetically allow the emission pathway.