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Author(s): C. J. Tavares
M. V. Castro
E. S. Marins
A. P. Samantilleke
S. Ferdov
L. Rebouta
M. Benelmekki
M. F. Cerqueira
P. Alpuim
E. Xuriguera
J. P. Rivière
D. Eyidi
M. F. Beaufort
A. Mendes
Title: Effect of hot-filament annealing in a hydrogen atmosphere on the electrical and structural properties of Nb-doped TiO 2 sputtered thin films
Issue Date: 2012
Abstract: In this work Nb-doped TiO2 thin films were deposited by d.c.-pulsed reactive magnetron sputtering at 500 °Cfrom a composite target with weight fractions of 96% Ti and 4% Nb, using oxygen as reactive gas. In order toenhance the conductive properties, the as-deposited samples were treated in vacuum with atomic hydrogenat a substrate temperature of 500 °C. The atomic hydrogen flow was generated by a hot filament, inside ahigh-vacuum chemical vapour deposition reactor, at a temperature of 1750 °C. In order to optimise the hydrogenhot-wire treatments, the H2 pressure was varied between 1.3 and 67 Pa, the treatment time was monitoredbetween 1 and 5 min and the hot-filament current was changed between 12 and 17 A. Darkconductivity was measured as a function of temperature and its value at room temperature was extrapolatedand used to assess the effect of the hydrogen annealing on the charge transport properties. A two-order ofmagnitude increase in dark conductivity was typically observed for optimised hydrogen treatments(10 Pa), when varying the hydrogen pressure, resulting in a minimum resistivity of ~3× 103 cm atroom temperature. The maximum amount of atomic H incorporation in oxygen vacancies was determinedto be ~5.7 at.%. Carrier mobility and resistivity were also investigated using Hall effect measurements. Correlationsbetween structural and electrical properties and the hydrogen treatment conditions are discussed.The purpose of these films is to provide a transparent and conductive front contact layer for a-Si based photovoltaics,with a refractive index that better matches that of single and tandem solar cell structures. This canbe achieved by an appropriate incorporation of a very small amount of cationic doping (Nb5+) into the titaniumdioxide lattice.
Subject: Engenharia química
Chemical engineering
Scientific areas: Ciências da engenharia e tecnologias::Engenharia química
Engineering and technology::Chemical engineering
Related Information: info:eu-repo/grantAgreement/FCT - Fundação para a Ciência e Tecnologia/Programa de Financiamento Plurianual de Unidades de I&D/FCOMP-01-0124-FEDER-022677/PROJECTO ESTRATÉGICO - UI 511 - 2011-2012/PEst-C/EQB/UI0511/2011
Document Type: Artigo em Revista Científica Internacional
Rights: restrictedAccess
Appears in Collections:FEUP - Artigo em Revista Científica Internacional

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