<title>Optical response of very thin As-Se films</title>

Abstract

Thin chalcogenide (As-S, As-Se, Ge-Se, etc.) films find applications in many branches of modern optics: for design of optical systems operating in VIS and IR, as recording material for holographic storage, or as inorganic photoresists, etc. Very thin films are included in multi-layered CD-R and DVD structures for improvements of their performance and increase of storage capacity. That is why developments of different methods for determination of optical constants (<i>n</i> - refractive index, <i>k</i> - extinction coefficient and <i>d</i> - physical thickness) best adapted for concrete optical problems are still needed. Recently we have presented a method for (<i>n, k, d</i>) evaluation of very thin metal or semiconductor films from spectrophotometric data. Here we present investigation of the optical constants of vacuum deposited As-Se thin layers with <i>d</i> between 15 and 30 nm. The dispersion of the complex refractive index is studied in the spectral range of 400 - 1000 nm. The obtained results are interpreted within the frame of single oscillator Wemple-DiDomenico model. Comparison is made with data on thicker evaporated layers. We demonstrate the importance of the analysis of the uncertainties in (<i>n, k, d</i>) determination for the adequate choice of the film physical thickness.