Toward a Systematic Understanding of Photodetectors Based on Individual Metal Oxide Nanowires

The Journal of Physical Chemistry C (Impact Factor: 4.77). 09/2008; 112:14639-14644. DOI: 10.1021/jp804614q


We present a set of criteria to optimize photodetectors based on n-type metal oxide nanowires and a comparison methodology capable of overcoming the present lack of systematic studies dealing with such devices. The response of photoconductors is enhanced following different fabrication strategies, such as diminishing the distance between the electrical contacts, increasing the width of the photoactive area, or improving the electrical mobility of the nanomaterials. The validity of the theoretical background is verified by experimental results obtained with devices based on ZnO nanowires. The performances of our devices show that the normalized gain of single ZnO nanowire-based photodetectors exceeds those of thin films.

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    • "These differences can be fully explained by taking into account the strong influence of surface-mediated electron–hole separation effects in nano-size materials [26]: charge separation slows down the electron–hole recombination times Fig. 4. (a) Photocurrent generated at different light intensities (˚ ph ) and bias voltages (V bias ). (b) Summary of the photocurrent response as a function of photon flux (˚ ph ), where the slope is a direct measurement of g ph , after geometry (W,L) and bias voltage (V bias ) correction [45]. (and thus the response times), leading to larger photocurrent values. "
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    Sensors and Actuators B Chemical 06/2015; DOI:10.1016/j.snb.2015.06.069 · 4.10 Impact Factor
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    • "The normalized photoconductive gain is thus independent of the device geometry and the experimental conditions. Our fabricated device has a gain of 10 6 , which is lower than that reported by (Soci et al. 2007) (gain of the order of 10 8 ) and (Chen et al. 2013) (gain of the order of 10 7 ), but higher than that reported by (Prades et al. 2008) (gain of the order of 10 4 ). However, when the experimental conditions are taken into account, our results of normalized gain is at least an order of magnitude higher than those reported earlier. "
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    ABSTRACT: On account of their large surface-to-volume ratio, nanowires contain an extremely high density of surface states which can lead to significantly enhanced photocarrier lifetimes resulting in persistent photoconductivity. There are reports that attribute the high photoconductive gain of ZnO nanowire-based photodetectors to hole trapping and de-trapping following oxygen adsorption and desorption from the nanowire surface. Through this work we provide experimental evidence of the role of surface and defects in carrier dynamics, resulting in enhanced photoresponse. ZnO nanowires with an average length of about 20 μm and diameters in the range of 60-80 nm were used in this experiment. Using intensity and temperature dependence of the rise and decay rate of photocurrent, we present a detailed analysis that provides an estimate of the activation energies of carrier trapping mechanisms. The high gain ZnO nanowire photodetector was sensitive to photoexcitation at or below 370 nm corresponding to the band-edge absorption profile of ZnO. At an incident wavelength of 370 nm and at a bias field of 5 kV/cm, it was found that the maximum responsivity is over 105 A/W corresponding to an extremely high photoconductive gain of the order of 106. This corresponds to a normalized photoconductive gain of 4 × 10−3 m2V−1.
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    • "Accordingly, we adopted the Γn, physically defined as the product of η, τ, and μ (i.e., Γn = ητμ) [45,48]. As the τμ product is an intrinsic quantity determining photocarrier transport efficiency [42], for a constant η, Γn offers the same physical meaning as τμ, and its intrinsic property can exclude the effects of device dimension and experimental condition. "
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