Characterization of nitrogen doped p-type ZnO thin films prepared by reactive ion beam sputter deposition

Abstract

Nitrogen doped ZnO (ZnO:N) thin films have been successfully prepared by reactive ion beam sputter deposition. The ZnO:N thin films show a preferred growth orientation along the (002) direction regardless of nitrogen flow rates. Raman spectroscopy analysis shows nitrogen related local vibration modes at 275 and 576cm−1 in addition to the ZnO E2 (high) mode at 436cm−1, indicating a successful incorporation of nitrogen into the ZnO. Both of the peak intensities of 275 and 576cm−1 reach a maximum after post-growth annealing at 500°C. ZnO:N deposited with a 0.5sccm nitrogen flow rate exhibits p-type conductivity with a hole concentration of 2.1×1017/cm3 and a mobility of 3cm2V−1s−1 after annealing at 500°C. Conversion to p-type conductivity was not observed on ZnO:N deposited with higher nitrogen flow rates. The p-type conductivity remains stable after it was stored at ambient conditions for more than two months. The p-type ZnO:N thin film is transparent in the visible range with a transmittance larger than 83%. SIMS analysis indicates that nitrogen concentration of less than 1.2at.% results in the successful preparation of p-type ZnO:N. ZnO:N deposited with higher nitrogen concentration results in n-type conductivity which is likely due to the formation of molecular nitrogen replacing oxygen sites that act as double donors (N2)O.