Enhanced photosensitivity in sol–gel derived 20GeO2:80SiO2 thin films |
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Authors: | Rajni K Pita SC Tjin SF Yu CH Kam |
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Institution: | (1) Photonics Research Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore, 639798, Singapore |
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Abstract: | We investigate the photosensitivity of binary 20GeO2:80SiO2 (germanosilicate) inorganic films. The samples have been fabricated by the sol–gel spin-coating method and the densification
has been performed by rapid thermal annealing at various temperatures ranging from 500 °C to 1000 °C. The –OH absorption bands
in the Fourier-transform infrared (FTIR) spectra and the refractive-index data show that the films annealed below 900 °C are
porous and the films annealed at 900 °C and above are dense. An ultraviolet (UV) KrF laser at 248 nm has been used to induce
the change in the refractive index of the samples. We have achieved a large refractive-index change (Δn) of 0.0098 after UV
illumination in excess of 1 min for our dense germanosilicate films. This UV-induced refractive-index change is attributed
to the formation of GeE’/SiE’ centers from Ge–Ge/Si–Si (neutral oxygen monovacancy) and Ge2+ centers and to the creation of oxygen deficiency related defects. From our experiments, the oxygen deficiency related defects
correspond to the absorption band at 620–740 cm-1 in the FTIR spectra and these are the defects which make a large contribution to Δn. The attenuation coefficient of the as-deposited
and UV-illuminated dense samples is about 0.42 dB/cm at 1550 nm. For porous samples, UV exposure has densified the samples
to some extent.
PACS 82.50.Hp; 71.23.Cq; 81.20.Fw |
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Keywords: | |
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