Pulsed laser deposited amorphous chalcogenide and alumino-silicate thin films and their multilayered structures for photonic applications

Abstract

Amorphous chalcogenide and alumino-silicate thin films were fabricated by the pulsed laser deposition technique. Prepared films were characterized in terms of their morphology, chemical composition, and optical properties. Multilayered thin film stacks for reflectors and vertical microcavities were designed for telecommunication wavelength and the window of atmosphere transparency (band II) at 1.54μm and 4.65μm, respectively. Bearing in mind the benefit coming from the opportunity of an efficient wavelength tuning or, conversely, to stabilize the photoinduced effects in chalcogenide films as well as to improve their mechanical properties and/or their chemical durability, several pairs of materials from pure chalcogenide layers to chalcogenide/oxide layers were investigated. Different layer stacks were fabricated in order to check the compatibility between dissimilar materials which can have a strong influence on the interface roughness, adhesion, density, and homogeneity, for instance. Three different reflector designs were formulated and tested including all-chalcogenide layers (As40Se60/Ge25Sb5S70) and mixed chalcogenide-oxide layers (As40Se60/alumino-silicate and Ga10Ge15Te75/alumino-silicate). Prepared multilayers showed good compatibility between different material pairs deposited by laser ablation despite the diversity of chemical compositions. As40Se60/alumino-silicate reflector showed the best parameters; its stop band (R>97% at 8° off-normal incidence) has a bandwidth of ~100nm and it is centered at 1490nm. The quality of the different mirrors developed was good enough to try to obtain a microcavity structure for the 1.5μm telecommunication wavelength made of chalcogenide layers. The microcavity structure consists of Ga5Ge20Sb10S65 (doped with 5000ppm of Er3+) spacer surrounded by two 10-layer As40Se60/Ge25Sb5S70 reflectors. Scanning and transmission electron microscopies showed a good periodicity, great adherence and smooth interfaces between the alternating dielectric layers confirming a suitable compatibility between the different materials.