Low power deposition of the polycrystalline CuxO film with a high mobility and a low hole concentration by radio-frequency magnetron sputtering of a Cu2O target

Abstract

Copper oxide (CuxO) thin films were prepared by radio-frequency magnetron sputtering with a Cu2O target. The sputtering power was varied from 40 W to 80 W while the working pressures (WPs) were 3–10 mtorr. Deposition rates, surface morphologies, carrier concentrations, carrier mobilities, optical characteristics, bandgaps and crystallinities of the deposited films were investigated. The preferential orientations of the films were Cu2O(111) and CuO(-111). A higher WP can lead to a significant increase in the Cu2O(111) phase and the size of the grain nanoclusters. A higher sputtering power can exhibit a higher hole mobility and a lower hole concentration. The average transmittances in the visible light range and optical bandgaps of the CuxO films were 33–50% and 2.6–2.7 eV. After a post annealing process at 300 °C for 1 h in air, the nanocluster size of the CuxO film prepared at the power of 80 W with WP of 5 mtorr can be increased from 40 nm to 70 nm. Meanwhile, a high mobility of 81.4 cm2/V s, a low hole concentration of 4.2 × 1013 cm−3, and a low density of states of 5 × 1013 cm−3eV−1 can be simultaneously obtained. Besides, a CuxO/ZnO heterojunction diode showing rectifying characteristic was fabricated to verify the semiconductor characteristic of the deposited p-type CuxO film.