Photoconductivity of Ultrathin Zinc Oxide Films

Takahashi, Yasutaka; Kanamori, Masaaki; Kondoh, Akiko; Minoura, Hideki; Ohya, Yutaka

doi:10.1143/jjap.33.6611

Cited by 286 publications

(192 citation statements)

References 8 publications

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“…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 …”

mentioning

confidence: 99%

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: 99%

ZnO Nanowire UV Photodetectors with High Internal Gain

et al. 2007

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“…decrease in oxygen binding energy. This chemisorption effect on the surface of the films is negligible in the other ambient such as high vacuum, inert gases and nitrogen [26,27].…”

Section: Structural Propertiesmentioning

confidence: 94%

“…After heat treatment, the changes in resistivity of GZO film can be explained by the chemisorptions of oxygen species at the grain boundaries. In general, the chemisorption of oxygen species at the grain boundaries may act as trapping sites and form potential barriers [29] and thereby decrease in the carrier concentration. On the other hand, the oxygen species scatter along the grain boundaries and occupy the oxygen vacancies in the film.…”

Section: Electrical Propertiesmentioning

confidence: 99%

Resistivity Stability of Ga Doped ZnO Thin Films with Heat Treatment in Air and Oxygen Atmospheres

Rao¹,

Kumar²

2012

JCPT

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The effect of annealing in air and oxygen on structural, electrical and optical properties of gallium doped ZnO thin films was investigated. The X-ray diffraction patterns showed that the films were highly preferentially oriented along (002) plane. After the heat treatment in air and oxygen environments, the intensity of (002) peak was apparently improved. It was found that heat treatment in air atmospheres lead to increase in surface roughness of the film. The GZO films annealed in oxygen at 673 K exhibited low resistivity of 4.21 × 10 -3 Ω·cm, while the resistivity of film annealed in air showed a slightly higher value of 7.14 × 10 -3 Ω·cm. In addition to this, all films have good optical transmittance about 80% in the visible region. It is found from the photoluminescence studies that the broad visible emissions in GZO films originated from the intrinsic shallow traps (V Zn ) and deep level vacancies (Z ni , O Zn and V O ).

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“…The conductivity of ZnO is extremely sensitive to UV light exposure. Basically, the photosensitivity in ZnO is regulated by chemisorption of oxygen [15][16][17][18][19]. In the absence of UV light, oxygen molecules get adsorbed on the surface as negatively charged ions by confining the free electrons, thereby create a depletion layer with low conductivity near the surface:…”

Section: Uv Detection Mechanism Of Zno Thin Films and Nanostructuresmentioning

confidence: 99%

“…In addition, outstanding physical and chemical properties of ZnO nanostructures such as large surface area, radiation hardness [12], superior spatial resolution [13] and high electron mobility provide a platform for versatile applications such as in food processing, sterilization of medical equipment, research laboratories, semiconductor processing industry etc., where an installation of UV detector is highly required. In addition, ZnO is also highly desired for thin film transistors, light emitting diodes, solar cells, surface acoustic wave and energy harvesting devices [14][15]. Herein, synthesis of ZnO thin films/nanostructures and study of their UV detection behavior were systematically carried out.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet photodetection characteristics of Zinc oxide thin films and nanostructures

Ghosh

Das

Tripathy

et al. 2016

IOP Conf. Ser.: Mater. Sci. Eng.

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mbar pressure. Post-deposition rapid thermal annealing of ZnO thin films were carried out at 1000°C for 600sec. ZnO nanostructures (nanowires/nanorods) were hydrothermally grown by using equimolar solution of Zinc nitrate and hexamethyltetramine. Morphology of ZnO thin films and nanostructures were investigated using scanning electron microscope. A comparative study on the ultraviolet photodetection behaviour of ZnO thin films and nanostructures were carried out by adopting current-voltage measurement technique at room temperature. ZnO annealed films have shown relatively lower transient photocurrent decay as compared to asdeposited film, which may be due to the faster evacuation of the charge carries. However, in case of ZnO nanorods transient photocurrent decay is relatively slow than that of nanowires, which is attributed to delayed readsorption of oxygen molecules onto the nanorods surface due to its larger width.

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Photoconductivity of Ultrathin Zinc Oxide Films

Cited by 286 publications

References 8 publications

ZnO Nanowire UV Photodetectors with High Internal Gain

ZnO Nanowire UV Photodetectors with High Internal Gain

Resistivity Stability of Ga Doped ZnO Thin Films with Heat Treatment in Air and Oxygen Atmospheres

Ultraviolet photodetection characteristics of Zinc oxide thin films and nanostructures

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