Understanding aging in chalcogenide glass thin films using precision resonant cavity refractometry

Abstract

Chalcogenide glass (ChG) thin films have a wide range of applications in planar photonics that rely on the stability of their optical properties. However, most methods do not provide quantitative optical property data at sufficiently high resolution. We have employed a resonant cavity refractometry technique capable of detecting refractive index changes down to 10[superscript -6] refractive index unit (RIU) to study the aging, or sub-T[subscript g] structural relaxation kinetics, of Ge[subscript 23]Sb[subscript 7]S[subscript 70]ChG. Our study reveals that the refractive index (RI) change due to aging tends to follow stretched exponential behavior, with stretch exponents and rate of index change dependent on initial glass treatment. Thermally annealed devices show the best stability, suggesting that thermal annealing is the appropriate post-deposition treatment method for obtaining stable ChG films.