The advantages of methanol-amine solvent mixtures in solution processing of Ge-Sb-S chalcogenide glass thin films

Abstract

We report on the substantial influence of methanol presence on the dissolution mechanism of Ge20Sb5S75 bulk glass with subsequent superior properties of thin films deposited from such solutions. Raman spectroscopy confirmed significant differences in structural features present in glass solutions prepared from pure amines (n-propylamine and n-butylamine) and their mixtures with methanol. The experiments with dissolved elemental sulfur and Ge25S75 glass analog proved that both antimony and methanol presence induce further splitting of the Ge4S104- cluster structure, which fundamentally affects the properties of deposited thin films. Significant structural and compositional differences were found not only in solutions and as-prepared samples, but also after thin films' thermal treatment (hard baking up to 210 degrees C). The as-prepared thin films deposited from amine-methanol mixtures possessed the exact composition of source bulk glass while thin films of other solvent formulations exhibited sulfur deficiency. The annealing up to 210 degrees C only highlighted this difference. As a result of the different structure of the thin films prepared in this way, the other benefits of methanol addition were found, namely an increase in the refractive index by approx. 0.1 independent of the annealing temperature, or a lower thermally induced thickness contraction (up to 7.5 %).