Study of oxide/metal/oxide thin films for transparent electronics and solar cells applications by spectroscopic ellipsometry

Mihaela Girtan,Laura Hrostea,Mihaela Boclinca,Beatrice Negulescu

doi:10.3934/matersci.2017.3.594

Mihaela Girtan, Laura Hrostea + Show 2 more

Open Access

https://doi.org/10.3934/matersci.2017.3.594

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Abstract

A comprehensive study of a class of Oxide/Metal/Oxide (Oxide = ITO, AZO, TiO2 and Bi2O3, Metal = Au) thin films was done by correlating the spectrophotometric studies with the ellispometric models. Films were deposited by successive sputtering from metallic targets In:Sn, Zn:Al, Ti and Bi in reactive atmosphere (for the oxide films) and respective inert atmosphere (for the metallic Au interlayer films) on glass substrates. The measurements of optical constants n—the refractive index and k—the extinction coefficient, at different incident photon energies for single oxide films and also for the three layers films oxide/metal/oxide samples were made using the spectroscopic ellipsometry (SE) technique. The ellipsometry modelling process was coupled with the recorded transmission spectra data of a double beam spectrophotometer and the best fitting parameters were obtained not only by fitting the n and k experimental data with the dispersion fitting curves as usual is practiced in the most reported data in literature, but also by comparing the calculated the transmission coefficient from ellipsometry with the experimental values obtained from direct spectrophotometry measurements. In this way the best dispersion model was deduced for each sample. Very good correlations were obtained for the other different thin films characteristics such as the films thickness, optical band gap and electrical resistivity obtained by other measurements and calculation techniques. The ellipsometric modelling, can hence give the possibility in the future to predict, by ellipsometric simulations, the proper device architecture in function of the preferred optical and electrical properties.

Highlights

ITO (Indium Tin Oxide) is a critical raw material mostly used as transparent electrode [1,2,3,4,5,6] in many applications such as plastic electronics, flexible solar cells, screens, etc
The apparently phase-separation like morphology for the TiO2/Au/TiO2 sample can be attributed to the fact that the top TiO2 film is very thin, much thinner, compared to the other samples, due to the scanning electron microscopy penetration depth, the top image of the three layer sample, the partially image of the gold layer can be visible through the top layer
A complete study of the optical and electrical properties of single oxide layer and oxide/metal/oxide (Oxide = ITO, AZO, TiO2 and Bi2O3, Metal = Au) three layers was done by spectrophotometry, ellipsometry and four probe electrical measurements

Summary

Introduction

ITO (Indium Tin Oxide) is a critical raw material mostly used as transparent electrode [1,2,3,4,5,6] in many applications such as plastic electronics, flexible solar cells, screens, etc. The huge development of these technologies and the limited resources of Indium require the replacement or the reduction of the necessary quantity ITO for such kind of applications [7,8,9,10,11,12,13,14,15,16]. Spectroscopic ellipsometry (SE) provides a widely applicable method for determining accurate characterization of optical and electrical transport properties of thin films multi-layers structures, in when the multilayer of device structure, is of critical importance to their effective implementation [20,21]

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