Structure and properties of spin-coated Ge_25S_75 chalcogenide thin films

Abstract

Amorphous chalcogenide thin films of Ge25S75 composition have been deposited by spin-coating technique. Optical properties of thin films were investigated by spectroscopic ellipsometry in UV-MIR spectral range. Obtained results prove increase of thin films refractive index in the transparent region and decrease of their thickness with increasing annealing temperature implying densification of the glass structure. Short wavelength absorption edge is shifting to lower energies (red shift) with increasing annealing temperature. Decreasing organic molecules content with increasing temperature of annealing was observed in MIR part of extinction coefficient and verified by Raman spectroscopy and EDS. Raman spectra also gave evidence of thermo-induced structural polymerization and decomposition of organic salts molecules yielding thin films with structure similar to the structure of the source bulk glass.

Exposure enhanced photoluminescence of CdS0.9Se0.1quantum dots embedded in spin-coated Ge25S75thin films

“…The Ge 25 S 75 ChG is non-toxic 40 and the thin lms were successfully deposited by spin-coating technique only recently. 31 The doped Ge 25 S 75 thin lms deposited by spin-coating technique were of good optical quality, well transparent in VIS and NIR and maintained PL of the QDs. The structural changes in structure of doped spin-coated thin lms were induced by UV lamp light exposure.…”

“…Thin lms annealed above 150 C are more structurally polymerized and with signicantly decreased content of organic residuals. 31 Thus, the observed photosensitivity is probably connected with organic residuals content and level of structural polymerization.…”

“…31 For doping of Ge 25 S 75 chalcogenide glass thin lms with prepared CdS 0.9 Se 0.1 QDs it is necessary to mix both components without precipitation in mixed solution. Thus, the CdS 0.9 Se 0.1 QDs were salts.…”

“…Thus, the CdS 0.9 Se 0.1 QDs were salts. 26,31 Due to the over-stoichiometry of S in Ge 25 S 75 bulk glass, the BA chalcogenide glass solution also contain free sulfur fragments, which were also found in BA solutions of Srich As-S chalcogenide glasses. 25 Those dissolution products and BA solvent are probably reacting with CdS 0.9 Se 0.1 QDs, which is reected in decrease of their PL intensity.…”

“…Thickness decrease can be explained by thermal decomposition of present AAGS salts connected with releasing of organic solvent residuals and ongoing structural polymerization. Previously it was conrmed that these salts start to decompose at $120 C. 31 The decomposition process should be practically completed at 210 C, 31 when the Ge 25 S 75 thin lm annealed at 210 C has $48% of as-prepared thin lm thickness. The data also proves that doping and UV exposure treatment have no signicant effect on the thickness of studied thin lms.…”