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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 14 — Jul. 5, 2010
  • pp: 14836–14841
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Photoconductive enhancement of single ZnO nanowire through localized Schottky effects

Ming-Wei Chen, Cheng-Ying Chen, Der-Hsien Lien, Yong Ding, and Jr-Hau He  »View Author Affiliations


Optics Express, Vol. 18, Issue 14, pp. 14836-14841 (2010)
http://dx.doi.org/10.1364/OE.18.014836


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Abstract

We demonstrated the Au nanoparticle (NP) decoration as an effective way to enhance both photocurrent and photoconductive gain of single ZnO nanowire (NW) photodetectors (PDs) through localized Schottky effects. The enhancement is caused by the enhanced space charge effect due to the existence of the localized Schottky junctions under open-circuit conditions at the NW surfaces, leading to a more pronounced electron-hole separation effect. Since the band-bending under illumination varies relatively small for an Au NP-decorated ZnO NW, the decay of gain is less prominent with increased excitation power, demonstrating the feasibility for a PD to maintain a high gain under high-power illumination.

© 2010 OSA

For the surface modification, metal nanoparticles (NPs) have been used to form Schottky junctions on the NW surfaces [9

9. C. H. Lin, T. T. Chen, and Y. F. Chen, “Photocurrent enhancement of SnO2 nanowires through Au-nanoparticles decoration,” Opt. Express 16(21), 16916–16922 (2008). [CrossRef] [PubMed]

,18

18. V. P. Zhdanov, “nm-sized metal particles on a semiconductor surface, Schottky model, etc,” Surf. Sci. 512(1-2), L331–L334 (2002). [CrossRef]

], modify the work function [19

19. H. Chen, H. Z. Zhang, L. Fu, Y. Chen, J. S. Williams, C. Yu, and D. P. Yu, “Nano Au-decorated boron nitride nanotubes: Conductance modification and field-emission enhancement,” Appl. Phys. Lett. 92(24), 243105 (2008). [CrossRef]

], and induce the charge transfer [20

20. Y. Mori and H. Kohno, “Resistance switching in a SiC nanowire/Au nanoparticle network,” Nanotechnology 20(28), 285705 (2009). [CrossRef] [PubMed]

] to achieve the better performances of NW-based devices with specific functions. In this letter, we show the feasibility of enhancing both the photocurrent and the photoconductive gain by the Au NP decoration at the surfaces of a single ZnO NW UV PD for the first time. The enhancement is due to the enhanced space charge effect via the formation of the localized Schottky junctions under open-circuit conditions at the NW surfaces, resulting in a more pronounced electron-hole separation effect.

ZnO NWs were prepared by heating the mixed ZnO and C powders (6.6 g: 3.3 g) in the furnace at 930 °C for 1 hour using the vapor-liquid-solid method. NWs were then transferred to Si substrates with a 200-nm-thick SiO2 layer. NWs were adhered to the substrate by Van der waals force. Ti/Au (10nm/70nm) electrodes for contacting ZnO NWs were defined by photolithography process and deposited by an electron gun evaporator. The devices were annealed at 400 °C for 30 seconds in order to obtain Ohmic contacts. Au NPs were sputtered on the ZnO NWs using a JEOL JFC-1600 coater at low current (~10 mA) for 20 seconds. Microstructures of Au NP-decorated ZnO NW were examined using a JEOL 4000EX transmission electron microscope (TEM) operating at 400 kV with a nominal point-to-point resolution of 0.18 nm. Morphological observation was conducted with an ELIONIX-7500 electron beam lithography system operating at 50 kV with a nominal point-to-point resolution of 2 nm. Photocurrent was measured under the illumination of a He-Cd laser with a wavelength of 325nm (Model: IK3552R-G of Kimmon KOMA Co. Ind.).

A low-magnification TEM image of an NP-decorated NW is shown in Fig. 1(a)
Fig. 1 (a) Low-magnification HRTEM image of a NP-decorated NW. (b) HRTEM image of a NP-decorated NW showing the distribution of Au NPs (dark spherical regions). (c) An HRTEM image of a pristine NW. (d) An HRTEM image at the interface of NPs and an NW.
. The fringes are known as thickness contours and are commonly observed in TEM specimens of NWs because NWs are cylinder-shaped. A high-magnification TEM image shows a uniform distribution of NPs with sizes of a few nm (dark spherical regions) on the NW surfaces, as shown in Fig. 1(b). The coverage rate of randomly distributed NPs is ~60%. Figure 1(c) shows a high resolution TEM (HRTEM) image of the NW without any NP, confirming that the phase of the NWs is wurtzite-structured ZnO. The measured interplanar distance of 0.26 nm corresponds to the ZnO(0002) planes, indicating that the NWs grew preferentially along the c-axis direction [21

21. J. H. He, C. H. Ho, C. W. Wang, Y. Ding, L. J. Chen, and Z. L. Wang, “Growth of crossed ZnO nanorod networks induced by polar substrate surface,” Cryst. Growth Des. 9(1), 17–19 (2009). [CrossRef]

]. Figure 1(d) shows a cross-sectional HRTEM image of the NW and the NPs. The measured interplanar distances of 0.20 nm and 0.24 nm correspond to the Au(200) and Au(111) planes, respectively. By examining the interface of Au and ZnO in Fig. 1(d), there is no intermediate phase formed between Au and ZnO, indicating that there is no chemical reaction after Au NPs are sputtered on ZnO NWs.

The inset in Fig. 2(a)
Fig. 2 (a) I-V curves of a single ZnO NW PD with Au NP decoration under UV illumination with the different power. The inset in (a) is the SEM image of a single ZnO NW PD. The comparison of the I-V curves between the pristine and the Au NP-decorated ZnO NW PDs under illumination with the power of (b) 10 mW, (c) 20 mW, and (d) 30 mW.
shows the SEM image of a single ZnO NW PD with Au-NP decoration. The diameter of the NW is ~100 nm, and the spacing between the electrodes is 2.4 μm. Photocurrent and dark current of the Au NP-decorated ZnO NW PDs are shown in Fig. 2(a). The linear behavior of I-V curves demonstrates an Ohmic contact between a single ZnO NW and the Ti/Au electrodes. The photocurrent increases with excitation power for the ZnO NW PDs with Au NP decoration. As compared with the pristine ZnO NW, a single NW with Au NP decoration shows a significant enhancement of the photocurrent, which is more prominent at the high excitation power, as shown in Fig. 2(b)-(d). The dark current for both the pristine and the Au-NP decorated NWs remains invariable at the range of 10−9 A, indicating that Au NPs do not produce new conductive routes at the surfaces of the ZnO NWs and the SiO2 substrates to contribute the dark current.

The effect of the photocurrent enhancement by Au NP decoration can be elucidated according to the band diagram of the ZnO NWs. It is known that the surface states of ZnO function as the adsorption sites. As shown in Fig. 3(a)
Fig. 3 (a) Schematic of the band diagram for the pristine and (b) the Au NP-decorated ZnO NW in dark.
, in air ambient, oxygen molecules adsorbing at these sites act as electron acceptors by capturing free electrons from ZnO in dark (O2 + e-→O2 -), which redistributes the spatial density of conducting carriers and thus forms a space charge region near the surfaces [22

22. J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]

25

25. S. J. Chang, T. J. Hsueh, I. C. Chen, and B. R. Huang, “Highly sensitive ZnO nanowire CO sensors with the adsorption of Au nanoparticles,” Nanotechnology 19(17), 175502 (2008). [CrossRef] [PubMed]

]. Under illumination, photo-generated holes tend to move to the surface through the surface electric field built by the space charge effect, and thereby the possibility for electron-hole recombination is reduced due to the spatial separation effect. The lifetime of electrons is further prolonged through the oxygen desorption by the neutralization of trapped holes and charged oxygen molecules at the surfaces (O2 - + h+→O2). The electron-hole separation effect induced by surface electric field explains the high photoconductive gain of a single ZnO NW PD [8

8. C. Soci, A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, and D. Wang, “ZnO nanowire UV photodetectors with high internal gain,” Nano Lett. 7(4), 1003–1009 (2007). [CrossRef] [PubMed]

,22

22. J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]

]. The surface band-bending and the width of the space charge region in dark increase with the density of surface states owing to charged oxygen molecules. Figure 3(b) depicts the band-bending diagram of a single ZnO NW after Au NP decoration. Though it is difficult to estimate the actual surface barrier between ZnO NWs and Au NPs since the charge distribution for metal NPs at the nanoscale might be different from that of typical Schottky model. However, the formation of a Schottky junction induced by Au NPs on ZnO NWs still can be understood by the difference in the work function of Au (5.10 eV) and the electron affinity of ZnO (4.3~4.6 eV) [26

26. K. Ip, G. T. Thaler, H. S. Yang, S. Y. Han, Y. J. Li, D. P. Norton, S. J. Pearton, S. W. Jang, and F. Ren, “Contacts to ZnO,” J. Cryst. Growth 287(1), 149–156 (2006). [CrossRef]

30

30. K. Jacobi, G. Zwicker, and A. Gutmann, “Work function, electron affinity and band bending of zinc oxide surfaces,” Surf. Sci. 141(1), 109–125 (1984). [CrossRef]

]. The uniformly distributed Au NPs on NW surfaces can be treated as a lot of localized Schottky junctions under open-circuit conditions, which enhances the surface band-bending. As compared with the pristine ZnO NW PDs, the spatial electron-hole separation effect is pronounced under UV illumination and thereby the electron lifetime is prolonged for an Au NP-decorated ZnO NW PD. Accordingly, the remaining photo-generated electrons in the NW core contribute to the increase of the photocurrent. In addition, the reason that the dark current does not decrease after Au NP decoration on NW might be due to the enhanced space charge effect, which results in the more concentrated conducting carriers in the inner core of the NWs, reducing the surface scattering.

In summary, we proposed that Au NP decoration at the NW surfaces can improve both the photocurrent and the photoconductive gain of a single ZnO NW PD. The underlying mechanism can be attributed to the fact that the pronounced electron-hole spatial separation effect via the formation of localized Schottky junctions under open-circuit conditions can be maintained under UV illumination for an Au NP-decorated ZnO NW. Besides, the enhanced space charge effect also results in an excitation power-insensitive gain, which is beneficial for a PD to maintain high gain even with the high-power excitation. This study demonstrates that Schottky metal NP decoration is effective to enhance both the photocurrent and photoconductive gain of NW PDs with high performance.

Acknowledgement

The research was supported by the National Science Council Grant No. NSC 96-2112-M-002-038-MY3, NSC 96-2622-M-002-002-CC3, and Aim for Top University Project from the Ministry of Education.

References and links

1.

J. H. He, S. Singamaneni, C. H. Ho, Y. H. Lin, M. E. McConney, and V. V. Tsukruk, “A thermal sensor and switch based on a plasma polymer/ZnO suspended nanobelt bimorph structure,” Nanotechnology 20(6), 065502–065506 (2009). [CrossRef] [PubMed]

2.

X. S. Fang, Y. Bando, U. K. Gautam, T. Y. Zhai, H. B. Zeng, X. J. Xu, M. Y. Liao, and D. Golberg, “ZnO and ZnS nanostructures: ultraviolet-light emitters, lasers, and sensors,” Crit. Rev. Solid State 34(3), 190–223 (2009). [CrossRef]

3.

X. S. Fang, Y. Bando, M. Y. Liao, U. K. Gautam, C. Y. Zhi, B. Dierre, B. D. Liu, T. Y. Zhai, T. Sekiguchi, Y. Koide, and D. Golberg, “Single-crystalline ZnS nanobelts as ultraviolet-light sensors,” Adv. Mater. 21(20), 2034–2039 (2009). [CrossRef]

4.

X. Y. Ma, J. W. Pan, P. L. Chen, D. S. Li, H. Zhang, Y. Yang, and D. R. Yang, “Room temperature electrically pumped ultraviolet random lasing from ZnO nanorod arrays on Si,” Opt. Express 17(16), 14426–14433 (2009). [CrossRef] [PubMed]

5.

W. Dai, Q. Yang, F. X. Gu, and L. M. Tong, “ZnO subwavelength wires for fast-response mid-infrared detection,” Opt. Express 17(24), 21808–21812 (2009). [CrossRef] [PubMed]

6.

H. Kind, H. Q. Yan, B. Messer, M. Law, and P. D. Yang, “Nanowire ultraviolet photodetectors and optical switches,” Adv. Mater. (Weinheim, Ger.) 14, 158–160 (2002).

7.

Y. Liu, Z. Y. Zhang, H. L. Xu, L. H. Zhang, Z. X. Wang, W. L. Li, L. Ding, Y. F. Hu, M. Gao, Q. Li, and L. M. Peng, “Visible light response of unintentionally doped ZnO nanowire field effect transistors,” J. Phys. Chem. C 113(38), 16796–16801 (2009). [CrossRef]

8.

C. Soci, A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, and D. Wang, “ZnO nanowire UV photodetectors with high internal gain,” Nano Lett. 7(4), 1003–1009 (2007). [CrossRef] [PubMed]

9.

C. H. Lin, T. T. Chen, and Y. F. Chen, “Photocurrent enhancement of SnO2 nanowires through Au-nanoparticles decoration,” Opt. Express 16(21), 16916–16922 (2008). [CrossRef] [PubMed]

10.

C. H. Lin, R. S. Chen, T. T. Chen, H. Y. Chen, Y. F. Chen, K. H. Chen, and L. C. Chen, “High photocurrent gain in SnO2 nanowires,” Appl. Phys. Lett. 93(11), 112115 (2008). [CrossRef]

11.

J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]

12.

J. B. K. Law and J. T. L. Thong, “Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time,” Appl. Phys. Lett. 88(13), 133114 (2006). [CrossRef]

13.

J. Zhou, Y. D. Gu, Y. F. Hu, W. J. Mai, P. H. Yeh, G. Bao, A. K. Sood, D. L. Polla, and Z. L. Wang, “Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization,” Appl. Phys. Lett. 94(19), 191103 (2009). [CrossRef] [PubMed]

14.

J. D. Prades, F. Hernandez-Ramirez, R. Jimenez-Diaz, M. Manzanares, T. Andreu, A. Cirera, A. Romano-Rodriguez, and J. R. Morante, “The effects of electron-hole separation on the photoconductivity of individual metal oxide nanowires,” Nanotechnology 19(46), 465501 (2008). [CrossRef] [PubMed]

15.

R. S. Aga, D. Jowhar, A. Ueda, Z. Pan, W. E. Collins, R. Mu, K. D. Singer, and J. Shen, “Enhanced photoresponse in ZnO nanowires decorated with CdTe quantum dot,” Appl. Phys. Lett. 91(23), 232108 (2007). [CrossRef]

16.

C. S. Lao, M. C. Park, Q. Kuang, Y. L. Deng, A. K. Sood, D. L. Polla, and Z. L. Wang, “Giant enhancement in UV response of ZnO nanobelts by polymer surface-functionalization,” J. Am. Chem. Soc. 129(40), 12096–12097 (2007). [CrossRef] [PubMed]

17.

N. Kouklin, “Cu-doped ZnO nanowires for efficient and multispectral photodetection applications,” Adv. Mater. 20(11), 2190–2194 (2008). [CrossRef]

18.

V. P. Zhdanov, “nm-sized metal particles on a semiconductor surface, Schottky model, etc,” Surf. Sci. 512(1-2), L331–L334 (2002). [CrossRef]

19.

H. Chen, H. Z. Zhang, L. Fu, Y. Chen, J. S. Williams, C. Yu, and D. P. Yu, “Nano Au-decorated boron nitride nanotubes: Conductance modification and field-emission enhancement,” Appl. Phys. Lett. 92(24), 243105 (2008). [CrossRef]

20.

Y. Mori and H. Kohno, “Resistance switching in a SiC nanowire/Au nanoparticle network,” Nanotechnology 20(28), 285705 (2009). [CrossRef] [PubMed]

21.

J. H. He, C. H. Ho, C. W. Wang, Y. Ding, L. J. Chen, and Z. L. Wang, “Growth of crossed ZnO nanorod networks induced by polar substrate surface,” Cryst. Growth Des. 9(1), 17–19 (2009). [CrossRef]

22.

J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]

23.

J. H. He, C. H. Ho, and C. Y. Chen, “Polymer functionalized ZnO nanobelts as oxygen sensors with a significant response enhancement,” Nanotechnology 20(6), 065503–065508 (2009). [CrossRef] [PubMed]

24.

C. Y. Chen, C. A. Lin, M. J. Chen, G. R. Lin, and J. H. He, “ZnO/Al2O3 core-shell nanorod arrays: growth, structural characterization, and luminescent properties,” Nanotechnology 20(18), 185605 (2009). [CrossRef] [PubMed]

25.

S. J. Chang, T. J. Hsueh, I. C. Chen, and B. R. Huang, “Highly sensitive ZnO nanowire CO sensors with the adsorption of Au nanoparticles,” Nanotechnology 19(17), 175502 (2008). [CrossRef] [PubMed]

26.

K. Ip, G. T. Thaler, H. S. Yang, S. Y. Han, Y. J. Li, D. P. Norton, S. J. Pearton, S. W. Jang, and F. Ren, “Contacts to ZnO,” J. Cryst. Growth 287(1), 149–156 (2006). [CrossRef]

27.

B. J. Coppa, R. F. Davis, and R. J. Nemanich, “Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000-1),” Appl. Phys. Lett. 82(3), 400–402 (2003). [CrossRef]

28.

A. Kolmakov, D. O. Klenov, Y. Lilach, S. Stemmer, and M. Moskovits, “Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles,” Nano Lett. 5(4), 667–673 (2005). [CrossRef] [PubMed]

29.

V. Dobrokhotov, D. N. McIlroy, M. G. Norton, A. Abuzir, W. J. Yeh, I. Stevenson, R. Pouy, J. Bochenek, M. Cartwright, L. Wang, J. Dawson, M. Beaux, and C. Berven, “Principles and mechanisms of gas sensing by GaN nanowires functionalized with gold nanoparticles,” J. Appl. Phys. 99(10), 104302 (2006). [CrossRef]

30.

K. Jacobi, G. Zwicker, and A. Gutmann, “Work function, electron affinity and band bending of zinc oxide surfaces,” Surf. Sci. 141(1), 109–125 (1984). [CrossRef]

31.

J. A. Garrido, E. Monroy, I. Izpura, and E. Munoz, “Photoconductive gain modelling of GaN photoconductors,” Semicond. Sci. Technol. 13(6), 563–568 (1998). [CrossRef]

OCIS Codes
(000.2700) General : General science

ToC Category:
Detectors

History
Original Manuscript: April 21, 2010
Revised Manuscript: June 17, 2010
Manuscript Accepted: June 22, 2010
Published: June 28, 2010

Citation
Ming-Wei Chen, Cheng-Ying Chen, Der-Hsien Lien, Yong Ding, and Jr-Hau He, "Photoconductive enhancement of single ZnO nanowire through localized Schottky effects," Opt. Express 18, 14836-14841 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-14-14836


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References

  1. J. H. He, S. Singamaneni, C. H. Ho, Y. H. Lin, M. E. McConney, and V. V. Tsukruk, “A thermal sensor and switch based on a plasma polymer/ZnO suspended nanobelt bimorph structure,” Nanotechnology 20(6), 065502–065506 (2009). [CrossRef] [PubMed]
  2. X. S. Fang, Y. Bando, U. K. Gautam, T. Y. Zhai, H. B. Zeng, X. J. Xu, M. Y. Liao, and D. Golberg, “ZnO and ZnS nanostructures: ultraviolet-light emitters, lasers, and sensors,” Crit. Rev. Solid State 34(3), 190–223 (2009). [CrossRef]
  3. X. S. Fang, Y. Bando, M. Y. Liao, U. K. Gautam, C. Y. Zhi, B. Dierre, B. D. Liu, T. Y. Zhai, T. Sekiguchi, Y. Koide, and D. Golberg, “Single-crystalline ZnS nanobelts as ultraviolet-light sensors,” Adv. Mater. 21(20), 2034–2039 (2009). [CrossRef]
  4. X. Y. Ma, J. W. Pan, P. L. Chen, D. S. Li, H. Zhang, Y. Yang, and D. R. Yang, “Room temperature electrically pumped ultraviolet random lasing from ZnO nanorod arrays on Si,” Opt. Express 17(16), 14426–14433 (2009). [CrossRef] [PubMed]
  5. W. Dai, Q. Yang, F. X. Gu, and L. M. Tong, “ZnO subwavelength wires for fast-response mid-infrared detection,” Opt. Express 17(24), 21808–21812 (2009). [CrossRef] [PubMed]
  6. H. Kind, H. Q. Yan, B. Messer, M. Law, and P. D. Yang, “Nanowire ultraviolet photodetectors and optical switches,” Adv. Mater. (Weinheim, Ger.) 14, 158–160 (2002).
  7. Y. Liu, Z. Y. Zhang, H. L. Xu, L. H. Zhang, Z. X. Wang, W. L. Li, L. Ding, Y. F. Hu, M. Gao, Q. Li, and L. M. Peng, “Visible light response of unintentionally doped ZnO nanowire field effect transistors,” J. Phys. Chem. C 113(38), 16796–16801 (2009). [CrossRef]
  8. C. Soci, A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, and D. Wang, “ZnO nanowire UV photodetectors with high internal gain,” Nano Lett. 7(4), 1003–1009 (2007). [CrossRef] [PubMed]
  9. C. H. Lin, T. T. Chen, and Y. F. Chen, “Photocurrent enhancement of SnO2 nanowires through Au-nanoparticles decoration,” Opt. Express 16(21), 16916–16922 (2008). [CrossRef] [PubMed]
  10. C. H. Lin, R. S. Chen, T. T. Chen, H. Y. Chen, Y. F. Chen, K. H. Chen, and L. C. Chen, “High photocurrent gain in SnO2 nanowires,” Appl. Phys. Lett. 93(11), 112115 (2008). [CrossRef]
  11. J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]
  12. J. B. K. Law and J. T. L. Thong, “Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time,” Appl. Phys. Lett. 88(13), 133114 (2006). [CrossRef]
  13. J. Zhou, Y. D. Gu, Y. F. Hu, W. J. Mai, P. H. Yeh, G. Bao, A. K. Sood, D. L. Polla, and Z. L. Wang, “Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization,” Appl. Phys. Lett. 94(19), 191103 (2009). [CrossRef] [PubMed]
  14. J. D. Prades, F. Hernandez-Ramirez, R. Jimenez-Diaz, M. Manzanares, T. Andreu, A. Cirera, A. Romano-Rodriguez, and J. R. Morante, “The effects of electron-hole separation on the photoconductivity of individual metal oxide nanowires,” Nanotechnology 19(46), 465501 (2008). [CrossRef] [PubMed]
  15. R. S. Aga, D. Jowhar, A. Ueda, Z. Pan, W. E. Collins, R. Mu, K. D. Singer, and J. Shen, “Enhanced photoresponse in ZnO nanowires decorated with CdTe quantum dot,” Appl. Phys. Lett. 91(23), 232108 (2007). [CrossRef]
  16. C. S. Lao, M. C. Park, Q. Kuang, Y. L. Deng, A. K. Sood, D. L. Polla, and Z. L. Wang, “Giant enhancement in UV response of ZnO nanobelts by polymer surface-functionalization,” J. Am. Chem. Soc. 129(40), 12096–12097 (2007). [CrossRef] [PubMed]
  17. N. Kouklin, “Cu-doped ZnO nanowires for efficient and multispectral photodetection applications,” Adv. Mater. 20(11), 2190–2194 (2008). [CrossRef]
  18. V. P. Zhdanov, “nm-sized metal particles on a semiconductor surface, Schottky model, etc,” Surf. Sci. 512(1-2), L331–L334 (2002). [CrossRef]
  19. H. Chen, H. Z. Zhang, L. Fu, Y. Chen, J. S. Williams, C. Yu, and D. P. Yu, “Nano Au-decorated boron nitride nanotubes: Conductance modification and field-emission enhancement,” Appl. Phys. Lett. 92(24), 243105 (2008). [CrossRef]
  20. Y. Mori and H. Kohno, “Resistance switching in a SiC nanowire/Au nanoparticle network,” Nanotechnology 20(28), 285705 (2009). [CrossRef] [PubMed]
  21. J. H. He, C. H. Ho, C. W. Wang, Y. Ding, L. J. Chen, and Z. L. Wang, “Growth of crossed ZnO nanorod networks induced by polar substrate surface,” Cryst. Growth Des. 9(1), 17–19 (2009). [CrossRef]
  22. J. H. He, P. H. Chang, C. Y. Chen, and K. T. Tsai, “Electrical and optoelectronic characterization of a ZnO nanowire contacted by focused-ion-beam-deposited Pt,” Nanotechnology 20(13), 135701 (2009). [CrossRef] [PubMed]
  23. J. H. He, C. H. Ho, and C. Y. Chen, “Polymer functionalized ZnO nanobelts as oxygen sensors with a significant response enhancement,” Nanotechnology 20(6), 065503–065508 (2009). [CrossRef] [PubMed]
  24. C. Y. Chen, C. A. Lin, M. J. Chen, G. R. Lin, and J. H. He, “ZnO/Al2O3 core-shell nanorod arrays: growth, structural characterization, and luminescent properties,” Nanotechnology 20(18), 185605 (2009). [CrossRef] [PubMed]
  25. S. J. Chang, T. J. Hsueh, I. C. Chen, and B. R. Huang, “Highly sensitive ZnO nanowire CO sensors with the adsorption of Au nanoparticles,” Nanotechnology 19(17), 175502 (2008). [CrossRef] [PubMed]
  26. K. Ip, G. T. Thaler, H. S. Yang, S. Y. Han, Y. J. Li, D. P. Norton, S. J. Pearton, S. W. Jang, and F. Ren, “Contacts to ZnO,” J. Cryst. Growth 287(1), 149–156 (2006). [CrossRef]
  27. B. J. Coppa, R. F. Davis, and R. J. Nemanich, “Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000-1),” Appl. Phys. Lett. 82(3), 400–402 (2003). [CrossRef]
  28. A. Kolmakov, D. O. Klenov, Y. Lilach, S. Stemmer, and M. Moskovits, “Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles,” Nano Lett. 5(4), 667–673 (2005). [CrossRef] [PubMed]
  29. V. Dobrokhotov, D. N. McIlroy, M. G. Norton, A. Abuzir, W. J. Yeh, I. Stevenson, R. Pouy, J. Bochenek, M. Cartwright, L. Wang, J. Dawson, M. Beaux, and C. Berven, “Principles and mechanisms of gas sensing by GaN nanowires functionalized with gold nanoparticles,” J. Appl. Phys. 99(10), 104302 (2006). [CrossRef]
  30. K. Jacobi, G. Zwicker, and A. Gutmann, “Work function, electron affinity and band bending of zinc oxide surfaces,” Surf. Sci. 141(1), 109–125 (1984). [CrossRef]
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