Characterisation of thin films obtained by laser ablation of Ge28Se60Sb12 glasses

Films of nominal composition Ge₂₈Se₆₀Sb₁₂ were deposited on microscope slides by pulsed laser deposition (PLD), using either bulk or powdered glassy targets and a Nd:YAG laser (λ=266 nm). The films with thickness comprised between 400 and 800 nm showed a smooth and dense morphology. They were homogeneous in composition all over the samples with a composition somewhat deficient in selenium compared to the nominal one: Ge_28.1±0.3Se_56.1±0.1Sb_15.8±0.2 and Ge_29.0±0.3Se_55.5±0.1Sb_15.5±0.2 for films obtained from powdered glassy targets and bulk targets, respectively. The optical characteristics of the films were extracted from the transmission spectra recorded between 250 and 2500 nm. In particular, the refractive index at 1.5 μm was found to be 2.75±0.03, close to that of the bulk glass, as expected for dense films. The decrease in the optical band gap and the increase in the Urbach absorption edge with the film thickness were attributed to an increase in disorder.