Influence of oxygen growth pressure on laser ablated Cr-doped In 2O 3 thin films

Abstract

We present a systematic investigation of the effects of oxygen growth pressure on the structural, optical, and electrical properties of In 2O 3:Cr thin films grown by pulsed laser deposition. X-ray diffraction analysis showed increases in lattice constant from 10.103 Å to 10.337 Å, and in particle size from 13.9 nm to 35.5 nm as the oxygen growth pressure increased from 7.5 × 10 −6 Torr to 7.5 × 10 −3 Torr, respectively. The observed shift in the X-ray diffraction peaks to lower angles was assumed to be caused by the reduction in the lattice defect density, precisely oxygen vacancies. The optical transparency increased with partial oxygen pressure ( P O 2 ) , and an average transmittance of ∼85% was obtained at 7.5 × 10 −3 Torr. The films are highly conducting with resistivity as low as 2 × 10 −4 Ω cm and mobility as high as 133 cm/V s. Temperature dependent resistivity measurements in the 45 < T < 300 K temperature range reveal that films grown at 7.5 × 10 − 6 ≤ P O 2 ≤ 7.5 × 10 − 4 Torr exhibit negative temperature coefficient of resistivity (TCR) below approximately T = 60 K, T = 120 K, T = 160 K; then positive TCR in the temperature intervals 60 < T < 300 K, 120 < T < 300 K, and 160 < T < 300 K, respectively. This suggests that two disparate mechanisms govern electrical dc transport in the two temperature regions. Film grown at P O 2 of 7.5 × 10 −3 Torr displayed typical semiconducting behavior with negative TCR in the whole temperature region.