Investigation on Structural, Optical and Electrical Properties of Pure and Nitrogen-Doped Zinc Oxide Films on Gallium Nitride Substrates: A Template-Assisted Physical Evaporation Approach

A one micron thick pure zinc oxide (ZnO) and nitrogen doped zinc oxide (N-ZnO) films, were fabricated on p-type, pristine (non-porous) and porous gallium nitride (GaN) substrates using a radio frequency (RF) sputtering technique at room temperature. The doping medium is nitrogen gas, which has a flow rate that ranges from 0 to 10 sccm (0 sccm refers to pure ZnO). Ultraviolet (UV) assisted photo electrochemical etching technique was employed to etch the wafer surface and develop porous GaN substrate. High-quality ZnO films were grown with ZnO powder as the target material under vacuum conditions. The X-ray diffraction (XRD) analysis confirms that the films grown on GaN possess a hexagonal wurtzite structure. For N-ZnO films, the UV-visible cut-off wavelength shifts towards the blue region. The root mean square (RMS) roughness of N-ZnO films, measured using atomic force microscopy (AFM), was found to decrease with increasing N-doping concentration. The lowest roughness value of 1.1 nm was observed for the 10 sccm sample, while the highest roughness of 3.4 nm was recorded for the pure ZnO film. The N-ZnO films was found to exhibit p-type conductivity as determined by Hall measurements using Van der Pauw method and the higher value of carrier concentration obtained for the nitrogen gas flow rate of 10 sccm, was 7.99 x 1018 cm-3.