Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization

Several, nearly-1-µ<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula>-thick, pure, unhydrogenated amorphous-sili...

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Autores principales: Emilio Márquez, Juan J. Ruíz-Pérez, Manuel Ballester, Almudena P. Márquez, Eduardo Blanco, Dorian Minkov, Susana M. Fernández Ruano, Elias Saugar
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spelling oai:doaj.org-article:0ebc5b8c66e84f9288485abf11e804db2021-11-25T17:16:02ZOptical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization10.3390/coatings111113242079-6412https://doaj.org/article/0ebc5b8c66e84f9288485abf11e804db2021-10-01T00:00:00Zhttps://www.mdpi.com/2079-6412/11/11/1324https://doaj.org/toc/2079-6412Several, nearly-1-µ<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula>-thick, pure, unhydrogenated amorphous-silicon (<i>a</i>-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the normal-incidence transmission of such a samples and on the adoption of the inverse-synthesis method, by using a devised Matlab GUI environment. The so-far existing limiting value of the thickness-non-uniformity parameter, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><mi>d</mi></mrow></semantics></math></inline-formula>, when optically characterizing wedge-shaped layers, has been suppressed with the introduction of the appropriate corrections in the expression of transmittance. The optical responses of the H-free RFMS-<i>a</i>-Si thin films investigated, were successfully parameterized using a single, Kramers–Krönig (KK)-consistent, Tauc–Lorentz oscillator model, with the inclusion in the model of the Urbach tail (TLUC), in the present case of non-hydrogenated <i>a</i>-Si films. We have also employed the Wemple–DiDomenico (WDD) single-oscillator model to calculate the two WDD dispersion parameters, dispersion energy, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi mathvariant="normal">d</mi></msub></semantics></math></inline-formula>, and oscillator energy, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi>so</mi></msub></semantics></math></inline-formula>. The amorphous-to-crystalline mass-density ratio in the expression for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi mathvariant="normal">d</mi></msub></semantics></math></inline-formula> suggested by Wemple and DiDomenico is the key factor in understanding the refractive index behavior of the <i>a</i>-Si layers under study. The value of the porosity for the specific rf-magnetron sputtering deposition conditions employed in this work, with an Ar-pressure of ~4.4 Pa, is found to be approximately 21%. Additionally, it must be concluded that the adopted TLUC parameterization is highly accurate for the evaluation of the UV/visible/NIR transmittance measurements, on the H-free <i>a</i>-Si investigated. Finally, the performed experiments are needed to have more confidence of quick and accurate optical-characterizations techniques, in order to find new applications of <i>a</i>-Si layers in optics and optoelectronics.Emilio MárquezJuan J. Ruíz-PérezManuel BallesterAlmudena P. MárquezEduardo BlancoDorian MinkovSusana M. Fernández RuanoElias SaugarMDPI AGarticleamorphous semiconductorsoptical propertiesdielectric functionthin-film characterizationTauc–Lorentz modelTauc–Lorentz–Urbach modelEngineering (General). Civil engineering (General)TA1-2040ENCoatings, Vol 11, Iss 1324, p 1324 (2021)
institution DOAJ
collection DOAJ
language EN
topic amorphous semiconductors
optical properties
dielectric function
thin-film characterization
Tauc–Lorentz model
Tauc–Lorentz–Urbach model
Engineering (General). Civil engineering (General)
TA1-2040
spellingShingle amorphous semiconductors
optical properties
dielectric function
thin-film characterization
Tauc–Lorentz model
Tauc–Lorentz–Urbach model
Engineering (General). Civil engineering (General)
TA1-2040
Emilio Márquez
Juan J. Ruíz-Pérez
Manuel Ballester
Almudena P. Márquez
Eduardo Blanco
Dorian Minkov
Susana M. Fernández Ruano
Elias Saugar
Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
description Several, nearly-1-µ<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula>-thick, pure, unhydrogenated amorphous-silicon (<i>a</i>-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the normal-incidence transmission of such a samples and on the adoption of the inverse-synthesis method, by using a devised Matlab GUI environment. The so-far existing limiting value of the thickness-non-uniformity parameter, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><mi>d</mi></mrow></semantics></math></inline-formula>, when optically characterizing wedge-shaped layers, has been suppressed with the introduction of the appropriate corrections in the expression of transmittance. The optical responses of the H-free RFMS-<i>a</i>-Si thin films investigated, were successfully parameterized using a single, Kramers–Krönig (KK)-consistent, Tauc–Lorentz oscillator model, with the inclusion in the model of the Urbach tail (TLUC), in the present case of non-hydrogenated <i>a</i>-Si films. We have also employed the Wemple–DiDomenico (WDD) single-oscillator model to calculate the two WDD dispersion parameters, dispersion energy, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi mathvariant="normal">d</mi></msub></semantics></math></inline-formula>, and oscillator energy, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi>so</mi></msub></semantics></math></inline-formula>. The amorphous-to-crystalline mass-density ratio in the expression for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>E</mi><mi mathvariant="normal">d</mi></msub></semantics></math></inline-formula> suggested by Wemple and DiDomenico is the key factor in understanding the refractive index behavior of the <i>a</i>-Si layers under study. The value of the porosity for the specific rf-magnetron sputtering deposition conditions employed in this work, with an Ar-pressure of ~4.4 Pa, is found to be approximately 21%. Additionally, it must be concluded that the adopted TLUC parameterization is highly accurate for the evaluation of the UV/visible/NIR transmittance measurements, on the H-free <i>a</i>-Si investigated. Finally, the performed experiments are needed to have more confidence of quick and accurate optical-characterizations techniques, in order to find new applications of <i>a</i>-Si layers in optics and optoelectronics.
format article
author Emilio Márquez
Juan J. Ruíz-Pérez
Manuel Ballester
Almudena P. Márquez
Eduardo Blanco
Dorian Minkov
Susana M. Fernández Ruano
Elias Saugar
author_facet Emilio Márquez
Juan J. Ruíz-Pérez
Manuel Ballester
Almudena P. Márquez
Eduardo Blanco
Dorian Minkov
Susana M. Fernández Ruano
Elias Saugar
author_sort Emilio Márquez
title Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
title_short Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
title_full Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
title_fullStr Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
title_full_unstemmed Optical Characterization of H-Free <i>a</i>-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization
title_sort optical characterization of h-free <i>a</i>-si layers grown by rf-magnetron sputtering by inverse synthesis using matlab: tauc–lorentz–urbach parameterization
publisher MDPI AG
publishDate 2021
url https://doaj.org/article/0ebc5b8c66e84f9288485abf11e804db
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