Toward Understanding the Role of V_Zn Defect on the Photoconductivity of Surface-Passivated ZnO NRs

Abstract

The point defects in ZnO nanorods (NRs) play a very crucial role in its photoconductivity (PC) properties, and thus it is essential to understand the sub-band gap carrier dynamics in order to have efficient ultraviolet (UV) photodetection. In order to understand the role of a dominant point defect, Zn vacancy (V Zn ), which is prevalent on the surface of the NRs, we employ a high-temperature annealing step in air and also an excess hydration step for one set of annealed NRs, each followed by a final surface passivation step by polyvinyl butyral. A comprehensive study on the photocurrent spectra, photocurrent transients under different sub-band gap excitations, and power dependence of photocurrent of aqueous chemically grown ZnO NRs treated under various conditions has been carried out and demonstrates the superiority (extraordinarily high and fast UV response) of the point defect rich but surface-passivated NRs as compared to ones with no or fewer V Zn defects. Further, good support of the major role of V Zn has been obtained from the PC results of a set of ZnO NRs treated in excess Zn with a concurrence from the enhanced UV-to-vis ratio. The experimental results in harmony with the reported theoretical calculations reveal that both trapping and/or recombination centers nature of an acceptor-like V Zn and their defect complexes are likely to be the most important roles played by the PC. The study offers new insight in understanding the advanced mechanism of PC of ZnO NRs controlled by V Zn -related sub-band gap defects.

ZnO UV Photodetectors Modified by Ag Nanoparticles Using All-Inkjet-Printing

“…To explain the changing mechanism of the I-V test results shown in Fig. 3, the energy levels of V O , V Zn, and O i -related defects are collected from references [27][28][29][30] in Fig. 4.…”

“…It can be concluded that the V O , V O + , V O 2+ , and V Zn defects are the hole traps [ 28 , 30 , 31 ]. The V Zn 2− and V Zn − defects are the electron trap and non-radiative recombination center [ 28 ], respectively. For Ag NP samples, the concentration of carrier trap is much less than that of the control sample according to the PL and XPS results in Fig.…”

“…− and V Zn − defects are the electron trap and nonradiative recombination center [28], respectively. For Ag NP samples, the concentration of carrier trap is much less than that of the control sample according to the PL and XPS results in Fig.…”

Effect of doping concentration on optical and electrical properties of intrinsic n-type ZnO (i-ZnO) and (Cu, Na and K) doped p-type ZnO thin films grown by chemical bath deposition method

“…Electrical properties of ZnO thin films doped with materials like Cu are very useful for optoelectronic applications [8] however efficiency of such films found limited due to formation of donor compensating point defects [9]. Coulomb interactions between dopant and acceptor-like defects, such as oxygen interstitial lead to bound complexes [10,11]. The combination of p-type and n-type material reduces the recombination rate of photo generated electrons and holes [12].…”

An Insight into the Influence of Donor Compensating Defects in Doped ZnO Thin Films

“…However, efficiency of dopant is limited due to formation of donor compensating point defects [2]. Coulombic interactions between the dopant and acceptor-like defects, such as oxygen interstitial (O i ) and zinc vacancy (V Zn ), lead to bound complexes [3][4][5][6]. Furthermore, it is shown that these complexes, rather than isolated impurities, dominate the electrical properties of trivalent cation doped ZnO.…”