Tuning of defects in vertical ZnO/CuO axial nanowire for efficient UV-A photodetection

Vertical ZnO/CuO axial nanowire (NW) arrays were fabricated by using glancing angle deposition technique inside the Radio Frequency (RF) magnetron sputtering system. A post annealing treatment of vertical ZnO/CuO axial NWs was performed in air from 200 °C to 900 °C temperature. Field emission scanning electron microscope imaging shows vertically well aligned NW structure. X-ray diffraction analysis showed improvement in crystalline structure, with increasing annealing with 400 °C sample showing the minimum dislocation density. The annealed sample at 400 °C (in air) shows high photoresponse as compared to other samples signifying reduction in defect states as also observed from photoluminescence analysis. The 400 °C sample showed the highest photocapacitance owing to the improvement in the interface. Moreover, the annealed vertical ZnO/CuO axial NW arrays at 400 °C showed a large responsivity (R) of 2.52 A W^-1, specific detectivity (D*) of 5.14 × 10¹¹Jones and noise equivalent power as low as 6.54 pW at +4 V respectively. Furthermore, the annealed 400 °C device showed fast response with equal rise and fall time of 0.02 ms at +4 V.