Na mole concentration dependence on optical p-type behaviors of Na-doped ZnO nanowires

•Na-doped ZnO nanowires were prepared by a simple hydrothermal technique at low growth temperature of about 90 °C.•Structural and optical analysis was systematically carried out to identify the influence of Na mole concentration in ZnO.•Low temperature PL spectra revealed the clear exciton bound to deeper acceptor (AD0X) peaks confirming the appearance of Na dopants inside ZnO NWs.•Temperature-dependent PL observations are well-matched to the value of the Varshini relation predictions.

We report the structural and optical features of Na-doped ZnO nanowires as a function of Na mole concentration to demonstrate the p-type conduction of Na-doped ZnO nanowires. The samples are prepared on RF-sputtered ZnO seed layers by using a simple hydrothermal method with sodium nitrate, zinc nitrate, and hexamethylenetetramine (HMTA) in an aqueous solution at low temperature (<90 °C). At first, the crystal structure of the c-axis orientation was analyzed using X-ray diffraction patterns. These exhibited a slight shift to lower values of the diffraction angle with decreasing Na mole concentration. To further verify the p-type behaviors of Na-doped ZnO nanowires, cryo-photoluminescence was employed at temperatures ranging from 10 to 300 K, corresponding to the clear appearance of excitons bound to a deeper acceptor (AD0X) and its LO phonon replicas.