The origin of visible photoluminescence from silicon oxide thin films prepared by dual-plasma chemical vapor deposition

In order to understand the radiative recombination mechanisms in silicon oxides, photoluminescence properties (PL) of H-rich amorphous silicon oxide thin films grown in a dual-plasma chemical vapor deposition reactor have been related to a number of stoichiometry and structure characterizations (x-ray photoelectron spectroscopy, vibrational spectroscopy, and gas evolution studies). The visible photoluminescence at room temperature from $\mathrm{a-}{\mathrm{SiO}}_x:\mathrm{H}$ matrixes with different compositions, including different bonding environments for H atoms, has been studied in the as-deposited and annealed states up to 900 °C. Three commonly reported PL bands centered around 1.7, 2.1, and 2.9 eV have been detected from the same type of $\mathrm{a-}{\mathrm{SiO}}_x:\mathrm{H}$ material, only by varying the oxygen content $\mathrm{(x}$ = 1.35, 1.65, and 2). Temperature quenching experiments are crucial to distinguish the 1.7 eV band, fully consistent with bandtail-to-bandtail recombination, from the radiative defect luminescence mechanisms attributed either to defects related to Si–OH groups (2.9 eV) or to oxygen-vacancy defects (2.1 eV). In the latter case, a red-shift of the PL peak energy as a function of annealing temperature is probably attributed to some matrix-induced strain effect.