Density-controlled and seedless growth of laterally bridged ZnO nanorod for UV photodetector applications

This study develops a density-controlled and seedless growth method for laterally bridged ZnO nanorods from Au electrode for use in metal-semiconductor-metal photodetector fabrication. The effect of pre-annealing process on suppressing vertical ZnO nanorods is systematically investigated by atomic force microscopy and scanning electron microscopy. The pre-annealing process is demonstrated to have direct influence on controlling vertical/lateral ZnO nanorod density and morphology. Interlaced and density-controlled ZnO nanorods with approximate single-crystalline structure can be directly grown from the side wall of pre-annealed Au electrode fingers without seed-layer. Through pre-annealing process, dark-current can be decreased from 4.99 x 10(-4) to 7.28 x 10(-7) A with an applied voltage of 1 V. Highly dense lateral ZnO nanorod-based photodetectors produce remarkable responsivity of 7.01 x 10(3) A/W and UV/visible rejection ratio of 281.21. Moreover, a high internal photoconductive gain (10(4)-10(5)) exists in the fabricated photodetectors. For a given bandwidth of 10 kHz and 1 V applied bias, the noise equivalent power of photodetectors with 0, 10, and 20 min pre-annealing periods are estimated to be 3.58 x 10(-13), 6.78 x 10(-13), and 4.86 x 10(-13) W, and correspond to normalized detectivity of 1.85 x 10(12), 1.17 x 10(12), and 1.99 x 10(12) cm Hz(0.5) W-1, respectively. This result may be attributed to internal photoconductive gain mechanism and high-density bridged ZnO nanorods. Our approach provides a simple and controllable method to fabricate high-performance ultraviolet photodetectors. (C) 2014 Elsevier B.V. All rights reserved.