Solvent-casting of Chalocogenide Glasses and Their Application in Mid-Infrared Optics
Speaker: Shanshan Song
Series: Final Public Orals
Location: Engineering Quadrangle J401
Date/Time: Friday, March 11, 2011, 10:30 a.m. - 12:30 p.m.
Spin-coating of chalcogenide glasses is a low-cost, scalable method to deposit optical grade thin films, which are ideal for visible and infrared applications. The compositional, optical and structural requirements imposed by useful device fabrication create a need for a more thorough understanding of solvent-chalcogenide interactions. A systematic method is developed to optimize glass dissolution and film deposition parameters based on those requirements. The importance of annealing conditions on optical and structural properties of spin-coated thin films is evaluated. Optical parameters are proven closely related to the amount of solvent residue, film density and glass structural network. Evaporation of excess solvent results in a more highly coordinated, denser glass network with higher index and lower absorption. Depending on the annealing temperature and time, index values within a certain range can be reproducibly obtained, enabling a pathway to materials optimization. This study also examines photo-induced modifications in spin-coated chalcogenide thin films. A giant photo-induced refractive index change in Ge-Sb-S films is reported. The mechanism for the change is proposed as being caused by photo-oxidation, i.e., the dangling bonds and homopolar bonds being transformed to Ge-O bonds. The photosensitive properties of chalcogenide glasses are then used to fine tune quantum cascade lasers by modifying an overlying chalcogenide cladding combined with deep-etched distributed Bragg gratings.