Absorption changes induced by UV-photon irradiation in Ge-doped SiO₂ thin films fabricated by plasma CVD method from tetraethoxysilane

Optical absorption changes induced by the irradiation of ultraviolet photons in Ge-doped SiO₂ thin films fabricated by plasma-enhanced chemical vapor deposition from tetraethoxysilane are studied. It is confirmed that the sample has a higher photo-sensitivity compared with bulk Ge-doped SiO₂ fabricated by conventional vapor-phase axial deposition. This is ascribed to the fact that the Ge E' center, a typical paramagnetic defect center in Ge-doped SiO₂ with a large optical absorption, is induced by the photon irradiation. Namely, the high photo-sensitivity originates from large concentrations of two oxygen-deficient precursors of the Ge E' center, the germanium lone pair center and the neutral oxygen vacancy. It is suggested that residual hydrogen from tetraethoxysilane also contributes to the induced optical absorption.