Conductivity of ZnO Nanowires, Nanoparticles, and Thin Films Using Time-Resolved Terahertz Spectroscopy

Baxter, Jason B.; Schmuttenmaer, Charles A.

doi:10.1021/jp064399a

Cited by 384 publications

(363 citation statements)

References 44 publications

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“…Electron transport in oriented crystalline nanowires is expected to be several orders of magnitude faster [448,449]. The transportation time is on the order of tens of microseconds as revealed by intensitymodulated photocurrent studies [450], by virtue of the high nanowire crystallinity and in particular an internal electric field that assists the exciton separation and charge collection [18,447].…”

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confidence: 99%

One-dimensional ZnO nanostructures: Solution growth and functional properties

2011

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One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, positioncontrolled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

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Section: Reproduced With Permissionmentioning

confidence: 99%

One-dimensional ZnO nanostructures: Solution growth and functional properties

2011

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“…It may also arise due to H−atoms in ZnO matrix. Due to large surface to volume ratio, surface related phenomenon is primarily governed by the adsorption and desorption of the chemisorbed oxygen at the surface of ZnO which may contribute an important role in the photoconductivity of nanostructures (thin films, nano− rod, nanowires and nanoparticles) [15][16][17][18][19][20]. These structures show high photoconductivity with slow dynamics.…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

Mishra

Srivastava

Prakash

et al. 2010

Opto-Electronics Review

146

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In the present paper, ZnO nanoparticles (NPs) with particle size of 20–50 nm have been synthesized by hydrothermal method. UV-visible absorption spectra of ZnO nanoparticles show absorption edge at 372 nm, which is blue-shifted as compared to bulk ZnO. Photoluminescence (PL) and photoconductive device characteristics, including field response, light intensity response, rise and decay time response, and spectral response have been studied systematically. The photoluminescence spectra of these ZnO nanoparticles exhibited different emission peaks at 396 nm, 416 nm, 445 nm, 481 nm, and 524 nm. The photoconductivity spectra of ZnO nanoparticles are studied in the UV-visible spectral region (366–691 nm). In spectral response curve of ZnO NPs, the wavelength dependence of the photocurrent is very close to the absorption and photoluminescence spectra. The photo generated current, Ipc = (Itotal - Idark) and dark current Idc varies according to the power law with the applied field IpcαVr and with the intensity of illumination IpcαIL r, due to the defect related mechanism including both recombination centers and traps. The ZnO NPs is found to have deep trap of 0.96 eV, very close to green band emission. The photo and dark conductivities of ZnO NPs have been measured using thick film of powder without any binder.

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“…Note that the ultrafast components of the photocarrier relaxation dynamics, such as the prompt electron-hole recombination and trapping, are not resolved in our measurements. 47,48 The results in air and under vacuum indicate that the oxygen adsorption to and desorption from the NW surface occurs in very short time (ns), suggesting that the desorbed oxygen molecules in air remain in close proximity to the surface and can be promptly readsorbed. 9 Figure 6c indicates that the oxygen readsorption to the surface and consequently the lowering of the dark current happen quickly after re-exposing the NWs to air; however, full recovery of the pristine conditions requires longer times, of the order of several minutes, due to the time required for oxygen molecules diffusion.…”

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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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Conductivity of ZnO Nanowires, Nanoparticles, and Thin Films Using Time-Resolved Terahertz Spectroscopy

Cited by 384 publications

References 44 publications

One-dimensional ZnO nanostructures: Solution growth and functional properties

One-dimensional ZnO nanostructures: Solution growth and functional properties

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

ZnO Nanowire UV Photodetectors with High Internal Gain

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