Structure and optical properties of hydrogenated silicon films prepared by plasma enhanced chemical vapour deposition

Hydrogenated silicon films are prepared in highly hydrogen diluted silane as the reactive gas in a conventional plasma enhanced chemical vapour deposition system. High resolution transmission electron microscope measurements show that the structure can be changed from pure amorphous to microcrystalline by variation of the technological parameters. We observed the best light-emitting properties in the samples with the structure of fine dispersed crystalline grains: crystallites with a sizes of 20-40 Angstrom embedded in the amorphous matrix. The optical gap of such films is around 2.0 eV. Combined studies of the photoluminescence and electroluminescence indicate an interband mechanism of the radiative recombination. Current-voltage characteristics of p-i-n structures on the basis of Si:H with fine grain structure indicate a tunnel mechanism of the current.