Photoluminescence and polarized photodetection of single ZnO nanowires

Fan, Zhiyong; Chang, Pai‐Chun; Lu, Jia Grac; Walter, Erich; Penner, Reginald M.; Lin, Chien‐Hung; Lee, Henry P.

doi:10.1063/1.1841453

Cited by 342 publications

(251 citation statements)

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“…Above the band gap energy, the photoconductivity is almost constant (note the semilogarithmic scale) up to the deep UV spectral region, while no photoresponse has been detected in the range from 1.5 to 3.2 eV. The absence of photoconduction upon visible light illumination testifies to the low defect levels, 17,18 such as oxygen vacancies in the ZnO NWs, which is supported by the low intrinsic electron concentration estimated above. The high spectral selectivity combined with high photosensitivity suggest the possibility of using ZnO NWs as "visible-blind" UV photodetectors for commercial, military, and space applications.…”

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confidence: 68%

“…Schematics of the NW energy band diagrams in dark and under illumination are displayed in parts b and c of Figure 2, respectively, illustrating the charge separation process of photogenerated electrons and holes under the intrinsic NW electric field and the occupation of surface states by photogenerated holes. In ZnO, it has been previously shown that the following trapping mechanism is governing the photoconduction in thin films 25 and NWs: 8,9,13,18,[26][27][28] in the dark (Figure 2b), oxygen molecules are adsorbed on the oxide surface and capture the free electrons present in the n-type oxide semiconductor [O 2 …”

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confidence: 99%

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ZnO Nanowire UV Photodetectors with High Internal Gain

et al. 2007

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ZnO nanowire (NW) visible-blind UV photodetectors with internal photoconductive gain as high as G ∼ 10 8 have been fabricated and characterized. The photoconduction mechanism in these devices has been elucidated by means of time-resolved measurements spanning a wide temporal domain, from 10 -9 to 10 2 s, revealing the coexistence of fast (τ ∼ 20 ns) and slow (τ ∼ 10 s) components of the carrier relaxation dynamics. The extremely high photoconductive gain is attributed to the presence of oxygen-related hole-trap states at the NW surface, which prevents charge-carrier recombination and prolongs the photocarrier lifetime, as evidenced by the sensitivity of the photocurrrent to ambient conditions. Surprisingly, this mechanism appears to be effective even at the shortest time scale investigated of t < 1 ns. Despite the slow relaxation time, the extremely high internal gain of ZnO NW photodetectors results in gain-bandwidth products (GB) higher than ∼10 GHz. The high gain and low power consumption of NW photodetectors promise a new generation of phototransistors for applications such as sensing, imaging, and intrachip optical interconnects.Because of its wide band gap (E g ) 3.4 eV), low cost, and ease of manufacturing, ZnO is emerging as a potential alternative to GaN in optoelectronic applications, 1 including light-emitting diodes, laser diodes, and photodetectors for the UV spectral range. In the past decade, the demonstration of a large variety of functional ZnO nanowire (NW) devices such as field effect transistors, 2,3 optically pumped lasers, 4,5 and chemical and biological sensors 6 have aroused growing interest in this material. 7 In particular, ZnO NW photodetectors and optical switches have been the subject of extensive investigations. [8][9][10][11][12][13][14][15][16][17][18] Despite the abundant research on NW photoconduction, 19 the two main factors contributing to the high photosensitivity of such nanostructures have been scarcely recognized: (1) the large surface-to-volume ratio and the presence of deep level surface trap states in NWs greatly prolongs the photocarrier lifetime; (2) the reduced dimensionality of the active area in NW devices shortens the carrier transit time. Indeed, the combination of long lifetime and short transit time of charge carriers can result in substantial photoconductive gain. [20][21][22] In this letter, we present ZnO NW photodetectors with large photoresponse; upon UV illumination at relatively low light intensities (I ∼ 10 µW/cm 2 ), the current in ZnO NWs increases by several orders of magnitude, which translates to a photoconductive gain of G > 10 8 . To elucidate the photoconduction mechanism that involves fast carrier thermalization and trapping at the NW surface and electronhole recombination at extended and localized states, we have studied the photoconductivity of ZnO NWs by time-resolved measurements and in different ambient conditions (e.g., in air or under vacuum). A physical model was developed to illustrate the origin of the photoconductive gain in ...

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ZnO Nanowire UV Photodetectors with High Internal Gain

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“…Additionally, it is also important to point out that in the particular case of ZnO nanowires the photo absorption spectrum typically has a narrow peak near the band edge in the exciton absorption region. 17,24 Consequently, V th also have its maximum value at the photoabsorption peak due to the highest increase in carrier density. This direct dependence of the V th with the energy of the incident light opens a new application of ZnO phototransistors because the gate voltage can be used to make the device more selective to certain frequencies.…”

Section: Resultsmentioning

confidence: 99%

ZnO UV photodetector with controllable quality factor and photosensitivity

et al. 2013

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ZnO nanowires have an enormous potential for applications as ultra-violet (UV) photodetectors. Their mechanism of photocurrent generation is intimately related with the presence of surface states where considerable efforts, such as surface chemical modifications, have been pursued to improve their photodetection capabilities. In this work, we report a step further in this direction demonstrating that the relative photosensitivity and quality factor (Q factor) of the photodetector are entirely tunable by an applied gate voltage. This mechanism enables UV photodetection selectivity ranging from wavelengths from tens of nanometers (full width at half maximum - FWHM) down to a narrow detection of 3 nm. Such control paves the way for novel applications, especially related to the detection of elements that have very sharp luminescence

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“…However, in the case of the samples studied here such a ratio -or rather its inverse -is a measure of internal lattice defects relative to the occurrence of chemisorbed oxygen, rather than any meaningful measure of 'crystallinity'. In any case it is clear that for ZC1-4 there is significant emission in the green-red regime (wavelength 475 -600 nm or energy 2.6 -2.1eV), a feature that has important bearing on the wavelength selective photoresponse of ZnO-based detectors [41][42][43][44].…”

Section: Photoluminescencementioning

confidence: 99%

Solution-based synthesis of cobalt-doped ZnO thin films

et al. 2012

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Publisher rights This is the author's version of a work that was accepted for publication in Thin Solid Films. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Thin Solid Films, Vol. 524, 01/12/2012 General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights.Take down policy The Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in the Research Portal that you believe breaches copyright or violates any law, please contact openaccess@qub.ac.uk. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT1 Solution-based synthesis of cobalt-doped ZnO thin films Sesha VempatiSchool of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UK, Amitha ShettyMaterials Research Center, Indian Institute of Science, Bangalore -560012, India. P. Dawson*School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UK, K. K. Nanda and S.B. KrupanidhiMaterials Research Center, Indian Institute of Science, Bangalore -560012, India.Corresponding author: p.dawson@qub.ac.uk AbstractUndoped and cobalt-doped (1-4 wt%) ZnO polycrystalline, thin films have been fabricated on quartz substrates using sequential spin-casting and annealing of simple salt solutions. X-ray diffraction (XRD) reveals a wurzite ZnO crystalline structure with high-resolution transmission electron microscopy showing lattice planes of separation 0.26 nm, characteristic of (002) planes.The Co appears to be tetrahedrally co-ordinated in the lattice on the Zn sites (XRD) and has a charge of +2 in a high-spin electronic state (X-ray photoelectron spectroscopy). Co-doping does not alter the wurzite structure and there is no evidence of the precipitation of cobalt oxide phases within the limits of detection of Raman and XRD analysis. Lattice defects and chemisorbed oxygen are probed using photoluminescence and Raman spectroscopy -crucially, however, this transparent semiconduc...

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Photoluminescence and polarized photodetection of single ZnO nanowires

Cited by 342 publications

References 21 publications

ZnO Nanowire UV Photodetectors with High Internal Gain

ZnO Nanowire UV Photodetectors with High Internal Gain

ZnO UV photodetector with controllable quality factor and photosensitivity

Solution-based synthesis of cobalt-doped ZnO thin films

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