Bipolar conductivity in amorphous Cu–Al–O thin films prepared by r.f. magnetron sputtering

Abstract

Bipolar electronic behavior has been demonstrated in amorphous Cu–Al–O thin films prepared on soda-lime glass substrate via radio frequency (r.f.) magnetron sputtering deposition technique. The tunable majority charge carrier type is as a result of the intentional adjustment of the percentage chemical composition of the material. Signs of Hall coefficients from Hall effect measurement and slopes of Mott-Schottky plots obtained for the films indicate the majority charge carrier type of each films. Negative Hall coefficient and a positive Mott-Schottky slope were obtained for the Al-rich film showing its n-type nature. Positive Hall coefficient and negative Mott-Schottky slope were obtained for the Cu-rich film showing its p-type nature. X-Ray Photoelectron Spectroscopy (XPS) was used to explain the variation in charge carrier type as a result of the adjustments made to the percentage chemical composition of the film. The I–V curves obtaine from simple devices fabricated show that the homojunction formed from the two films exhibit rectifying and photovoltaic properties. The rectifying behavior was studied between a bias of −1 V to +1 V. In addition, a VOC of 0.33 V, a JSC of 8.00 mA/cm2, an FF of 0.30 and a PCE of 0.79% were obtained from the photovoltaic device fabricated.