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Low-Voltage High-Performance UV Photodetectors: an Interplay between Grain Boundaries and Debye Length Renheng Bo, Noushin Nasiri, Hongjun Chen, Domenico Caputo, Lan Fu, and Antonio Tricoli ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b12321 • Publication Date (Web): 29 Dec 2016 Downloaded from http://pubs.acs.org on January 2, 2017
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ACS Applied Materials & Interfaces
Low-Voltage High-Performance UV Photodetectors: an Interplay between Grain Boundaries and Debye Length Renheng Bo1, Noushin Nasiri1, Hongjun Chen1, Domenico Caputo2, Lan Fu3, Antonio Tricoli1,* 1
Nanotechnology Research Laboratory, Research School of Engineering Australian National University, Canberra, Australia
2
Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
3
Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National Univer-
sity, Canberra, Australia.
Keywords: Visible-blind UV Photodetectors, Ultra-Low Voltage, Nanoparticle Networks, Surface Depletion, Grain Boundaries
Abstract Accurate detection of UV light by wearable low-power devices has many important applications including environmental monitoring, space to space communication, and defense. Here, we report the structural engineering of ultraporous ZnO nanoparticle networks for fabrication of very low-voltage high-performance UV photodetectors. Record high photo- to dark-current ratio of 3.3×105 and detectivity of 3.2×1012 Jones at ultra-low operation bias of 2 mV and low UV-light intensity of 86 µW⋅cm-2 are achieved by controlling the interplay between grain boundaries and surface depletion depth of ZnO nanoscale semiconductors. An optimal window of structural properties is determined by varying the particle size of ultraporous nanoparticle networks from 10 to 42 nm. We find that small electron-depleted nanoparticles (≤ 40 nm) are necessary to minimize the dark-current, however, the rise in photo-current is tampered with decreasing particle size due to the increasing density of grain boundaries. These findings reveal that nanoparticles with a size close to twice their Debye’s length are required for high phototo dark-current ratio and detectivity, while further decreasing their size decreases the photodetector performance.
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ACS Applied Materials & Interfaces
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Introduction Ultraviolet (UV) photodetectors based on wide bandgap semiconductors are attracting significant research and commercial interest.1-3 Besides the advantage of being inherently visible-blind, these materials enable novel designs and applications including devices’ topping4 and optoelectronic chemical sensing for environmental monitoring.5 Among most performing wide band gap semiconductors, zinc oxide offers some unique advantages, such as a room temperature bandgap of 3.37 eV (λ = 370 nm), low UV detection limits,6 low cost and high environmental tolerance.7 Photodetectors based on ZnO have been fabricated by several methods including chemical vapor deposition (CVD),8 thermal evaporation,9 sogel,7 pulsed laser deposition,10 electrochemical deposition10 and radio frequency magnetron sputtering.11 Recently, Hu et al.9 presented a wet-route self-assembly approach for ZnO/ZnS biaxial nanobelt films having low dark-current of 15.1 nA and high photo-current of up to 18 µA under a bias of 5 V and a UV light intensity of 910 µW.cm-2. Similar low dark-current and photo-current reaching 100 µA under 4×104 µW.cm-2 light intensity and an applied bias of 5 V have been achieved with CVD-grown ZnO nanowires.8 Very recently, ultraporous networks of ZnO nanoparticles have been demonstrated as a highly performing material for UV photodetectors, featured milliampere high photo-currents6 and picoampere dark-currents resulting in very high photo- to dark-current ratio of 3.4×105 at a bias of 5 V and light intensity of 86 µW.cm-2. This was attributed to the positive contribution of the high porosity and homogenous structural properties that facilitated O2 adsorption and desorption processes, and penetration of UV light.6, 12-13 Optimization of the properties of these nanoparticle networks bears the potential to further increase their performance for ultra-low voltage (
