Photocurrent in ZnO nanowires grown from Au electrodes

Keem, Kihyun; Kim, Hyunsuk; Kim, Gyu Tae; Lee, Jong Soo; Min, Byungdon; Cho, Kyoungah; Sung, Man Young; Kim, Sangsig

doi:10.1063/1.1756205

Cited by 301 publications

(197 citation statements)

References 11 publications

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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: 66%

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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confidence: 66%

ZnO Nanowire UV Photodetectors with High Internal Gain

et al. 2007

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“…In particular, fabrication of stable and rectifying metal contacts to ZnO remains a challenge despite numerous recent investigations. [1][2][3][4][5][6][7][8][9][10][11][12] A number of studies have addressed various possible fundamental mechanisms affecting Schottky barrier ͑SB͒ performance in ZnO, 1,5,9-13 but none have considered the role of both the surface and subsurface. Thus, while several studies have proposed that surface morphology, hydroxide ͑OH͒, and carbon surface contamination play a dominant role, none have considered the role of subsurface defects and impurities that could alter local carrier concentrations, depletion widths, and tunneling.…”

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confidence: 99%

Role of near-surface states in ohmic-Schottky conversion of Au contacts to ZnO

Mosbacker

Strzhemechny

White

et al. 2005

Applied Physics Letters

245

175

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A conversion from ohmic to rectifying behavior is observed for Au contacts on atomically ordered polar ZnO surfaces following remote, room-temperature oxygen plasma treatment. This transition is accompanied by reduction of the “green” deep level cathodoluminescence emission, suppression of the hydrogen donor-bound exciton photoluminescence and a ∼0.75eV increase in n-type band bending observed via x-ray photoemission. These results demonstrate that the contact type conversion involves more than one mechanism, specifically, removal of the adsorbate-induced accumulation layer plus lowered tunneling due to reduction of near-surface donor density and defect-assisted hopping transport.

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“…14-17͒ and ZnO nanostructures [18][19][20][21][22][23] where it was shown that photogenerated holes induce desorption of oxygen absorbed on the surface. Adsorbed oxygen acts as an electron trap and its release enhances the concentration of mobile electrons originating from the native doping and photoexcitation of the ZnO.…”

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confidence: 99%

Electronic memory effects in diodes from a zinc oxide nanoparticle-polystyrene hybrid material

Verbakel

Meskers

Janssen

2006

Applied Physics Letters

144

118

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Current-voltage characteristics of diode structures with an active layer of a zinc oxide nanoparticle-polystyrene hybrid material (1:2 by weight) deposited by spin coating from solution were investigated. Aluminum and poly(3,4-ethylenedioxythiophene):polystyrene-sulfonate were used as electrodes. After a forming step, the conduction under reversed bias voltage can be raised or lowered in a gradual and reversible manner by applying forward and reverse bias voltages, respectively. Electrically induced switching between states with high and lower conductivities is possible on a time scale of 100ms and the conduction levels remain stable for over 1h.

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Photocurrent in ZnO nanowires grown from Au electrodes

Cited by 301 publications

References 11 publications

ZnO Nanowire UV Photodetectors with High Internal Gain

ZnO Nanowire UV Photodetectors with High Internal Gain

Role of near-surface states in ohmic-Schottky conversion of Au contacts to ZnO

Electronic memory effects in diodes from a zinc oxide nanoparticle-polystyrene hybrid material

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