Substrate bias influence on the properties of ZnO:Al and ZnO:Al,N films deposited by magnetron sputtering

ZnO-based wide bandgap semiconductor oxides with a bandgap 3.3 eV have unique optical and electrical properties that make it promising for transparent electronics, optoelectronics and solar cells [1]. Magnetron sputtering (MS) attracts our attention due to the great possibilities for the deposition oxide films with good film adhesion, high deposition rates, film uniformity and stable composition of the deposited films. Traditionally the substrate potential at MS is grounded. The negative or positive potential applied to substrate (substrate bias) can influence the film growth as well. As to single-doped ZnO:Al and codoped ZnO:Al,N films the influence of substrate bias on their structure, and optical and electrical properties has not been studied yet in detail. In this work, we focus on the investigation of indicated properties of thin films deposited on Si and glass substrates by radio frequency magnetron sputtering in a layer-by-layer regime. Sample characterization was carried out by traditional instruments: X-ray diffraction, EDX spectroscopy, Raman scattering, photoluminescence, IR Fourier transform spectrometry, optical and electrical measurements. The experimental results will be presented and discussed. Shortly, the best crystalline quality demonstrates ZnO:Al films grown with the highest negative voltage bias of -30V. We have found that applying a negative bias voltage to the substrate during film growth allows us to increase the conductivity of ZnO:Al films three times compared to zero-biased ZnO:Al films deposited at the same conditions. ZnO:Al,N films show very high specific resistivity due to acceptor complex formation. It must be noted that all deposited ZnO:Al and ZnO:Al,N films demonstrate a high transparency of over 80 % with an optical band gap in the range 3.34-3.42 eV for ZnO:Al films while ZnO:Al,N films demonstrate band gap near 3.15 eV.