Dielectric modelling of optical spectra of thin In2O3 : Sn films

• Published in: Journal of physics. D, Applied physics Vol. 35; no. 8; pp. 794 - 801
• Main Authors: Mergel, D, Qiao, Z
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.04.2002; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; General theory; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Theory, models, and numerical simulation; Grain boundaries; Drude model; Free electron model; Doping; Computerized simulation; Experimental study; Thin films; Tin additions; Dielectric function; Energy gap; Impurities; Modelling; Electronic transition; Indium oxides; Absorption spectra; Microstructure; Carrier density; Radiofrequency sputtering
• DOI: 10.1088/0022-3727/35/8/311
• ISSN: 0022-3727

Optical transmittance spectra of ITO films were simulated with a computer program based on dielectric modeling. The films were prepared by RF sputtering under various oxygen fluxes such that the carrier density varies from 3 OE 10 exp 19 to 1.5 OE 10 exp 21 cu cm. The dielectric function used is the sum of three types of electronic excitations: intraband transitions of tree electrons (Drude model), band gap transitions, and interband transitions into the upper half of the conduction band. The parameters of these excitations are evaluated as a function of the carrier density. The damping in the Drude term was modeled frequency-dependent to account for the low extinction coefficient observed in the visible spectral range. The parameters resulting from the optical measurements were compared with those from the electrical measurements. Both the optical mobility and carrier density are found to be higher than those of the respective electric parameters. These discrepancies are attributed to a pronounced microstructure with badly conducting grain boundaries. The refractive index at 550 nm decreases linearly with increasing electron concentration. This is due both to the shift of the plasma edge and the Burstein-Moss shift of the band edge. All band gap transitions go up to the Fermi level. (Author)