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.