Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time

Law, J. B. K.; Thong, John T. L.

doi:10.1063/1.2190459

Cited by 329 publications

(239 citation statements)

References 19 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 …”

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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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ZnO Nanowire UV Photodetectors with High Internal Gain

et al. 2007

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“…Room-temperature ultraviolet lasing [12] and piezoelectric nanogenerators based on ZnO nanowire arrays have been demonstrated [13]. Rectifying diodes of single ZnO nanobelt/nanowire-based devices [14] and a ZnO nanowire photodetector [15] were fabricated very recently.…”

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Piezoelectricity in ZnO nanowires: A first-principles study

Xiang¹,

Yang²,

Hou³

et al. 2006

Applied Physics Letters

187

126

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Hexagonal [0001] nonpassivated ZnO nanowires are studied with density functional calculations. The band gap and Young's modulus in nanowires which are larger than those in bulk ZnO increase along with the decrease of the radius of nanowires. We find ZnO nanowires have larger effective piezoelectric constant than bulk ZnO due to their free boundary. In addition, the effective piezoelectric constant in small ZnO nanowires doesn't depend monotonously on the radius due to two competitive effects: elongation of the nanowires and increase of the ratio of surface atoms. Although many studies on ZnO nanowires have been conducted, there are some important issues remained to be addressed. First, the mechanical properties, especially the Young's modulus of ZnO nanowires are on debate in the literature [16,17,18,19,20]. For instance, Chen et al. [16] showed that the Young' modulus of ZnO nanowire with diameters smaller than about 120 nm is significantly higher than that of bulk ZnO. However, the elastic modulus of vertically aligned [0001] ZnO nanowires with an average diameter of 45 nm measured by atomic force microscopy was found to be far smaller than that of bulk ZnO[17]. The second issue is about the electromechanical coupling in ZnO nanowires. The effective piezoelectric coefficient of individual (0001) surface dominated ZnO nanobelts measured by piezoresponse force microscopy was found to be much larger than the value for bulk wurtzite ZnO [21]. In contrast, Fan et al. showed that the piezoelectric coefficient for ZnO nanopillar with the diameter about 300 nm is smaller than the bulk values [22]. They suggested that the reduced electromechanical response might be due to structural defects in the pillars [22]. Whether the electromechanical coupling is enhanced or depressed in defect-free ZnO nanowires is not clear. Thirdly, although it is well known that the quantum confinement effect will decrease the band gap of passivated nanowires, the question that how the dangling bond in bare ZnO nanowires affects the band gap remains open. The fundamental study on these issues is crucial for developing future applications of ZnO nanowires.In this letter, we have studied the electronic, mechanical, and piezoelectric properties of [0001] ZnO nanowires using first-principles methods for the first time. We find that the band gap increases along with the decrease of the radius of ZnO nanowires due to the radial confinement. The Young's modulus of nanowires is larger than bulk ZnO, in agreement with the experimental results of Chen et al. [16]. The effective piezoelectric constant in ZnO nanowires is larger than that of bulk ZnO due to the free boundary of nanowires. Moreover, the effective piezoelectric constant in small ZnO nanowires doesn't depend monotonously on the radius due to two competitive effects.Our calculations are performed using the SIESTA package[23], a standard Kohn-Sham density-functional program using norm-conserving pseudopotentials and numerical atomic orbitals as basis sets. The local density approximation (LD...

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“…Many materials and structures including quantum dots [90][91][92], nanotubes [93][94][95][96], and nanowires [97][98][99] have been studied and considered to be good alternatives for silicon-based photodetectors. Interestingly, most of the 2D semiconductors are sensitive to light, heat, and ambient which makes them very attractive for applications in optoelectronic device sensing from infrared to the ultraviolet regime.…”

Section: Photodectorsmentioning

confidence: 99%

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

Sun¹,

Xu²,

Zhang³

et al. 2018

Crystals

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Two-dimensional (2D) semiconductors are thought to belong to the most promising candidates for future nanoelectronic applications, due to their unique advantages and capability in continuing the downscaling of complementary metal-oxide-semiconductor (CMOS) devices while retaining decent mobility. Recently, optoelectronic devices based on novel synthetic 2D semiconductors have been reported, exhibiting comparable performance to the traditional solid-state devices. This review briefly describes the development of the growth of 2D crystals for applications in optoelectronics, including photodetectors, light-emitting diodes (LEDs), and solar cells. Such atomically thin materials with promising optoelectronic properties are very attractive for future advanced transparent optoelectronics as well as flexible and wearable/portable electronic devices.

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Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time

Cited by 329 publications

References 19 publications

ZnO Nanowire UV Photodetectors with High Internal Gain

ZnO Nanowire UV Photodetectors with High Internal Gain

Piezoelectricity in ZnO nanowires: A first-principles study

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

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