Preparation and characterization of germanium oxysulfide glassy films for optics

Abstract

International audienceHomogeneous amorphous films in the GeS2-GeO2 system have been deposited by a rf sputtering technique. Optical characterizations have shown that the cut-off wavelength and the linear indices increase with an increase in the S/O ratio. Raman spectroscopy indicates the presence of new modes that can be assigned to intermediate germanium oxysulfide structural units. Photo-sensitivity of the oxysulfide films has been demonstrated for irradiation near the band-gap. Diffraction gratings inscribed using 488 nm exposure displayed a limited diffraction efficiency (≤3%) that weakens with a corresponding decrease in the glass S/O ratio

Aging process of photosensitive chalcogenide films deposited by electron beam deposition

“…The percentage of Ga atoms bonded to O was larger compared to that of Ge and As and the weakness of Ga-S compared to Ge-S and As-S bonds was proposed to explained this behavior. Nevertheless in our Ge 15 Sb 20 S 65 film, germanium atoms might be coordinated with both sulfur and oxygen and the formation of Ge-O could be related to the presence of tetrahedral units such as GeO 3 S, GeO 2 S 2 or GeOS 3 in agreement with Maurel et al [50,51]. Such a tendency of Ge atoms could provide a mechanism for incorporating in the glassy network the diffusing oxygen atoms, and, consequently, a way of reducing formation of oxidation crystallised products on the aged film surface.…”

“…While the mechanism of photooxidation of chalcogenides is still under discussion, previous works [46][47][48][49][50][51] suggest that photo-induced changes may be due to incorporation of oxygen in the glass matrix and to formation of covalent bonds with glass-forming elements, e.g. Ge-O or Ge-OH bonds at the surface in the case of Ge-Sb-S films.…”

“…Kohoutek et al [54] have reported the formation of As 2 O 3 crystals onto As-S film surface as result of oxidation after exposure of air, while the introduction of few percent of Sb allowed preventing such behavior onto As-Sb-S film surface. Photo-oxidation under irradiation at 633 nm was observed by Cardinal et al on germanium-sulfide films for which oxygen diffusion most probably occurs from the top of the film [50]. According to Tanaka et al the formation of GeO 2 crystals by illumination could not be expected on the surface of the Ge based films [49].…”

Processing and characterization of new oxysulfide glasses in the Ge–Ga–As–S–O system

“…Because of the presence of oxygen atoms in the glass network, one can expect contributions from the symmetric stretching of Ge-O-Ge bridging bonds around 420 cm À1 [20]. In accordance with our recent study on a more simple system such as GeS 2 -GeO 2 [8], the main band cannot be obtained by simple summation of GeS 2 vibrational features to the oxide spectra. The addition of a new band between 360 and 400 cm À1 , different from GeO 4 or GeS 4 tetrahedral sites, was necessary to correctly simulate the spectrum.…”

“…Raman spectroscopy was a useful tool to show the presence of new modes that were assigned to intermediate germanium oxysulfide structural units. Moreover, we have shown that it is possible to deposit amorphous films in the GeS 2 -GeO 2 system using a RF sputtering technique which can be considered as a fast quenching rate as compared to classical melt quench technique [8].…”