A dynamic optical constant extraction method for thin films with structural and optical-parametric justifications

An original fitting approach grounded on dynamic n ( lambda ) dispersion along with envelop based Connell-Lewis (C-L) relation for optical absorption was developed and implemented to extract the optical constants from experimental T ( lambda ) spectra of thin films. Thermal-vapor-deposited chalcogenide CdSe thin films having a thickness range of similar to 650-1550nm were chosen for this purpose. The interdependence of n ( lambda ) and k ( lambda ) in the analytical T ( lambda ) expression through the C-L equation partially mimics the Kramers-Kronig relation, which is a requirement for the optical constant to be physically meaningful. The average quadratic function within the measured spectral range was found to fall below 1%. On the contrary, a pronounced scattering in the relative difference spectra (similar to 10%) observed within a very narrow band of interference pattern was attributed to a systematic error and uncertainty in the spectral shape just above the absorption edge. The validity of the extracted optical and dimensional parameters was scrutinized in terms of microstructural and crystallographic measurements. The variation in packing density, estimated from the extracted n ( lambda ) spectra, commensurates with the temperature evolution of microstructural features. The bathochromic shifts in the split transition energies obtained from the extracted k ( lambda ) spectra were discussed satisfactorily in terms of the quantum threshold size effect. Although this fitting approach was applied only to a chalcogenide thin film, it is anticipated to be applicable to the other transparent thin films as well.