Semiconductive properties of anodic niobium oxides

 A.I. de Sá,^a,*C.M. Rangel,^a P. Skeldon,^b G.E. Thompson^b

 

^a DMTP/Electroquímica de Materiais, Instituto Nacional de Engenharia Tecnologia e Inovação, Paço do Lumiar, 22, 1649-038 Lisboa - Portugal

^b Corrosion and Protection Centre, School of Materials, The University of Manchester, P.O. Box 88, Manchester M60 1QD, UK

 

 

Abstract

The semiconductive properties of anodic niobium oxides formed at constant potential and constant current density to different final voltages have been examined by Mott-Schottky analysis.

Thin anodic oxides were formed on sputtered niobium specimens at constant potential in the range of 2.5 to 10 V_Ag/AgCl in a borate buffer solution. Thicker oxides were formed, also on sputtered niobium specimens, at a constant current density of 5 mA cm^-2 in 0.1 M ammonium pentaborate solution to final voltages of 10, 50 and 100 V. Capacitance measurements were performed in a borate buffer solution of pH 8.8, at a frequency range of 200 to 2000 Hz, at a sweep rate of 5 mV s^-1 from +2.5 to –1 V_Ag/AgCl.

The results obtained show n-type semiconductor behaviour with a carrier density in the range of 8 ´ 10¹⁸ – 6 ´ 10¹⁹ cm^-3 on films formed to 10 V. Thicker films showed lower carrier densities in the range of 1 ´ 10¹⁸ – 2 ´ 10¹⁸ cm^-3 with a calculated charge depletion layer of 33-36 nm.

Keywords: niobium oxides, anodic oxides, Mott-Schottky behaviour.

 

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*Corresponding author. E-mail address: Ana.Sa@ineti.pt