Conversion mechanism of conductivity and properties of nitrogen implanted ZnO single crystals induced by post-annealing

In this paper, the conversion mechanism of conductivity and properties of nitrogen (70 keV, 1 × 10¹⁶ cm⁻²) implanted ZnO single crystals induced by post-annealing in a temperature ranging from 500 °C to 800 °C have been investigated by Hall, Raman, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and low temperature photoluminescence (PL) measurements. The results indicate that the sample converts to p-type conductivity as annealed at 650 °C. For the as-implanted sample, different type of nitrogen (N) local states are detected, including substitutional N atom and N₂ molecules on O site [No and (N₂)o], N–O, N–H, and N–C complexes. However, their thermal stabilities display significant difference upon thermal annealing. Differing from the initial ZnO bulk, the low-temperature PL spectrum of the post-annealed N implanted ZnO sample consists of two dominant peaks located at 3.105 eV and 3.220 eV, respectively. The former is attributed to radiative electron transition from the conduction band to the Zn vacancy (V_Zn) acceptor level, and the latter is assigned to recombination of the donor–acceptor pair (DAP). Our results suggest that the V_Zn together with the No acceptors are responsible for p-type conductivity of N doped ZnO.