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.