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

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.