Investigation of the optical behavior of indium oxide thin films with the aid of spectroscopic ellipsometry technique

Abstract

Indium oxide thin films were deposited at different substrate temperatures onto silicon substrates using pulsed laser deposition technique. An optical model consisting of Tauc-Lorentz and Gaussian oscillators along with a surface roughness layer on top was used to fit the spectroscopic ellipsometry data in the range of photon energy 1.3–5 eV. Effect of interband transitions occurring in the range 3.67–4.82 eV was ensured by a combination of four Gaussian oscillators. Energy of these transitions as well as the band gap retrieved from ellipsometry analysis increased with the increment in substrate temperature. Band gap obtained from diffuse reflectivity measurements using Kubelka-Munk method depicted an exactly similar type of variation. Further, band gaps retrieved from Ellipsometry (3.51–3.93 eV) were more close to the bulk indium oxide band gap value (3.6 eV) than that obtained from Kubelka-Munk method (2.63–3.06 eV). Atomic force microscopy measurements provided further support to our analysis by producing surface roughness values that were closely related to that obtained from modeling. Band gap variation with the substrate temperature was correlated to incremental grain growth in the films as evident from atomic force microscopy, field emission scanning electron microscope and X-ray analysis.