Graphene/ZnO nanowire/graphene vertical structure based fast-response ultraviolet photodetector

time, and recovery speed of our UV detectors are 8 � 10 2 , 0.7s, and 0.5s, respectively, which are significantly improved compared to the conventional ZnO NWs photodetectors. The improved performance is attributed to the existence of Schottky barriers between ZnO NW and graphene electrodes. The graphene/ZnO NW/graphene vertical sandwiched structures may be promising candidates for integrated optoelectronic sensor devices. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4724208] ZnO, as a wide direct band gap (3.37eV) compound semiconductor with large exciton binding energy (60meV), has been widely investigated for its potential applications in optoelectronic devices, gas and chemical sensors. 1,2 Due to large surface-to-volume ratio, ZnO nanowires (NWs) exhibit highly susceptible photoelectric properties by means of electron-hole generation or recombination during ultraviolet (UV) illumination. Therefore, ZnO NWs have great potential in high sensitivity and fast-response UV sensors, 3 environmental monitors, and optical communications. 4 Recently, Hu et al. 5 reported ZnO NW based UV sensors using Schottky contact formed between ZnO and Pt electrode and the device performance such as the sensitive and UV response, is much higher than that of the traditional ZnO NW photoconductivity based UV sensors. The UV detectors based on Schottky barriers formed between ZnO NW and other metal electrodes, such as gold electrodes, have also been studied. 6,7 Nevertheless, metal electrodes are poor in transparency and can dramatically influence the absorption efficiency of the UV sensors. Graphene, a monolayer sp 2 carbon atoms with unique physical properties, such as high mobility and conductivity, 8 high optical transparency 9 and mechanical flexibility, 10 etc., has attracted great research interest recently. The high conductive and optical transparent properties make graphene an ideal candidate for the application in transparent electrode. The Schottky barrier is also expected to be existed at the interface between ZnO nanowire and graphene, and it has been utilized for light-emitting diodes 11 and transparent nanogenerators. 12 In this letter, we have fabricated a vertical sandwich structure of graphene/ZnO NW/graphene. We demonstrate the high performance of our ZnO NW based vertical UV photodetector due to the existence of Schottky barriers between graphene electrodes and ZnO NW. The current on-off ratio of the UV detector is up to 8 � 10 2 at a illumination power density of 50lw/lm 2 , the photocurrent

[1]  Jae-Young Choi,et al.  Fully Rollable Transparent Nanogenerators Based on Graphene Electrodes , 2010, Advanced materials.

[2]  C. Soci,et al.  ZnO nanowire UV photodetectors with high internal gain. , 2007, Nano letters.

[3]  Kai Yan,et al.  Site‐Specific Transfer‐Printing of Individual Graphene Microscale Patterns to Arbitrary Surfaces , 2011, Advanced materials.

[4]  Youfan Hu,et al.  Supersensitive, Fast‐Response Nanowire Sensors by Using Schottky Contacts , 2010, Advanced materials.

[5]  W. Zhang,et al.  Enhanced UV photoresponse from heterostructured Ag–ZnO nanowires , 2009 .

[6]  M. Aono,et al.  Giant Improvement of the Performance of ZnO Nanowire Photodetectors by Au Nanoparticles , 2010 .

[7]  S. Chang,et al.  A ZnO nanowire vacuum pressure sensor , 2008, Nanotechnology.

[8]  J. Kysar,et al.  Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene , 2008, Science.

[9]  G. Fudenberg,et al.  Ultrahigh electron mobility in suspended graphene , 2008, 0802.2389.

[10]  Bingxiao Liu,et al.  ZnO nanowire Schottky barrier ultraviolet photodetector with high sensitivity and fast recovery speed , 2011 .

[11]  B. L. Sharma,et al.  Metal--Semiconductor Schottky Barrier Junctions and Their Applications , 2012 .

[12]  M. Zacharias,et al.  Nanowire-based sensors. , 2010, Small.

[13]  Z. Liao,et al.  Controllable synthesis and characterization of tube brush-like ZnO nanowires produced via a simple chemical vapor deposition method , 2010 .

[14]  Z. Liao,et al.  Effect of surface states on electron transport in individual ZnO nanowires , 2007 .

[15]  O. Nur,et al.  Single nanowire-based UV photodetectors for fast switching , 2011, Nanoscale research letters.

[16]  R. Piner,et al.  Transfer of large-area graphene films for high-performance transparent conductive electrodes. , 2009, Nano letters.

[17]  Zhong Lin Wang,et al.  Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization. , 2009, Applied physics letters.

[18]  G. Qin,et al.  Multicolor graphene nanoribbon/semiconductor nanowire heterojunction light-emitting diodes , 2011, 1103.1754.

[19]  Rui Zhang,et al.  Strain dependent resistance in chemical vapor deposition grown graphene , 2011 .

[20]  E. Monroy,et al.  Wide-bandgap semiconductor ultraviolet photodetectors , 2003 .

[21]  J. Kennedy,et al.  UV and humidity sensing properties of ZnO nanorods prepared by the arc discharge method , 2009, Nanotechnology.

[22]  Z. Liao,et al.  Improved performance of ZnO nanowire field-effect transistors via focused ion beam treatment , 2011, Nanotechnology.

[23]  Zhenhua Ni,et al.  Raman Mapping Investigation of Graphene on Transparent Flexible Substrate: The Strain Effect , 2008 .