Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

Abstract

Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high 20 frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen 21 concentrations and structures were obtained. The transition from an amorphous to a crystalline material, 22 induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen fromthe films plays 23 an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of 24 hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced 25 crystallizationwas obtained on samples deposited at lower substrate temperatures. A correlation between these 26 measurements allowsto analyze the evolution of structuralproperties of the samples. The presence of voids in the 27 material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline 28 silicon thin films.