p-type Sodium-doped Zinc Oxide Nanowire Arrays Grown by High-pressure Pulsed Laser Deposition

Sodium-doped ZnO(ZnO:Na) nanowire arrays were grown with high-pressure pulsed laser deposition(HP-PLD). The influence of growth pressure and thickness of gold catalyst layer on the growth of ZnO:Na nanowires were systemically studied. It is found that c-orientated ZnO nanowire arrays grow on single crystal silicon substrates under the optimized condition, e.g. gold catalyst layer's thickness of 4.2 nm, growth pressure of 3.33×104 Pa and growth temperature of 875 ℃. X-ray diffraction pattern and X-ray photoelectron spectroscope analyses indicate that Na is introduced into ZnO nanowires successfully. Optical fingerprints of sodium-related acceptors in the low-temperature(15 K) photoluminescence spectrum are observed, such as neutral acceptor-bound exciton emission(3.356 eV, A0X), free-electron to neutral-acceptor emission(3.312 eV,(e, A0)), and donor-to-acceptor pair emission(3.233 eV, DAP). ZnO:Na nanowire arrays grown on ZnO:Al/sapphire substrates form the pn junction. The corresponding I-V curve measurements exhibit a clear rectifying behavior of pn homojunction, which further indicates that such ZnO:Na nanowire is of p-type conductivity.