Comparison of dispersion models in the optical characterization of As-S chalcogenide thin films

In this paper, the optical analysis of the As-S thin films prepared under different conditions is performed using three dispersion models for amorphous materials typically employed in practice. The Tauc-Lorentz (TL) model, Urbach-Cody-Lorentz (UCL) model and our model based on the parameterization of the density of electronic states (PDOS model) are namely used to determine the optical parameters of these films. Within the structural model of the As-S films, the existence of the optical constants profiles and overlayers on to the upper boundaries of these films are included. Dispersion and structural models are employed within the analysis based on a combination of variable angle spectroscopic ellipsometry and transmission spectrophotometry in conjunction with multi-sample modification. It is demonstrated that the TL model is not suitable for the optical characterization of the As-S thin films because of the absence of the Urbach tail. Furthermore, it is shown that both the UCL and PDOS models are satisfactory ones for the optical characterization of these films. Moreover, it is also shown that, using the PDOS dispersion model, one can evaluate the material parameters of these As-S films that correspond to the electronic band structure. (c) 2006 Elsevier B.V. All rights reserved.