P-Type highly conductive and transparent NdF3-doped tin oxide films prepared by dip coating

Abstract

Transparent p-type conducting oxide (TCO) films with high conductivity and transparency are in great need to couple with n-type TCO for various electro-optical devices. The purpose of the current study is to explore p-type TCO films with low electrical resistivity and high optical transmittance. We prepared NdF3-added SnO2 (NFTO) thin films, with 0 to 5mol% NdF3, on a glass substrate by sol–gel dip-coating and post-annealed at 475°C. Structural, optical and electrical properties of the resultant NFTO films were investigated. X-ray diffraction patterns indicate tetragonal rutile SnO2 structure with a preferred (110) orientation for all studied films. The absence of impurity peaks indicates that Nd and F atoms may completely dissolve in SnO2 lattice. All films showed excellent transmittance of 84.7 to 90.6% at a wavelength of 550nm. Optical band gap of the NFTO films reduces from 3.94eV for un-doped film to a minimum of 3.75eV for the film with 4mol% NdF3. We confirmed p-type conduction of NFTO films using both Hall-effect and Seebeck coefficient measurements. The film with 2mol% NdF3 shows the lowest electrical resistivity, 8.2×10−3Ωcm, the highest hole-concentration, 8.96×1019cm−3 and a Hall mobility of 9.74cm2V−1s−1. The developed p-type NdF3 added SnO2 TCO films can couple with n-type SnO2 TCO for homo-junctions, which will lead to wide applications in optoelectronics.