Structural evolution of nanocrystalline silicon thin films synthesized in high-density,low-temperature reactive plasmas

Abstract

Silicon thin films with a variable content of nanocrystalline phase weredeposited on single-crystal silicon and glass substrates by inductively coupledplasma-assisted chemical vapor deposition using a silane precursor withoutany hydrogen dilution in the low substrate temperature range from 100 to300 °C. The structural and optical properties of the deposited films are systematicallyinvestigated by Raman spectroscopy, x-ray diffraction, Fourier transform infraredabsorption spectroscopy, UV/vis spectroscopy, scanning electron microscopyand high-resolution transmission electron microscopy. It is shown that thestructure of the silicon thin films evolves from the purely amorphous phase to thenanocrystalline phase when the substrate temperature is increased from 100 to150 °C. It is found that the variations of the crystalline fractionfc, bonded hydrogencontent CH, optical bandgapETauc, film microstructureand growth rate Rd are closely related to the substrate temperature. In particular, at a substrate temperature of300 °C, the nanocrystalline Si thin films of our interest feature a high growth rate of1.63 nm s−1, a low hydrogen content of 4.0 at.%, a high crystalline fraction of 69.1%, a low opticalbandgap of 1.55 eV and an almost vertically aligned columnar structure with a mean grainsize of approximately 10 nm. It is also shown that the low-temperature synthesis ofnanocrystalline Si thin films without any hydrogen dilution is attributed to the outstandingdissociation ability of the high-density inductively coupled plasmas and effectiveplasma–surface interactions during the growth process. Our results offer a highlyeffective yet simple and environmentally friendly technique to synthesize high-qualitynanocrystalline Si films, vitally needed for the development of new-generation solar cellsand other emerging nanotechnologies.