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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 11 — May. 24, 2010
  • pp: 11821–11826
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High-response ultraviolet photodetector based on N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine and 2-(4-tertbutylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole

Q. Dai and X. Q. Zhang  »View Author Affiliations


Optics Express, Vol. 18, Issue 11, pp. 11821-11826 (2010)
http://dx.doi.org/10.1364/OE.18.011821


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Abstract

A high-performance heterojunction ultraviolet (UV) photodetector based on N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine (NPB) and 2-(4-tertbutylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) has been fabricated. The J-V characteristic curves of the device demonstrate a more than 4 orders of magnitude difference when illuminated under a 350 nm UV light and in the dark at + 3 V. The device exhibits high sensitivity in the 300–420 nm region with the peak located around 350 nm. A high photocurrent response of 4.5 A/W at +3 V under an incident intensity of 60 μW/cm2 was achieved. These results indicate that the NPB/PBD heterojunction structure device might be used as low-cost UV photodetectors.

© 2010 OSA

1. Introduction

Ultraviolet (UV) photodetectors have attracted much attention due their potential applications in areas such as environmental pollution monitoring, astrophysical analysis of solar and stellar spectra, aeronautic and astronautic materials research, solar UV and ozone layer studies, nondestructive testing of materials in industry, flame warning, gas sensing, and missile detection systems [1

1. M. Razeghi and A. Rogalski, “Semiconductor ultraviolet detectors,” J. Appl. Phys. 79(10), 7433 (1996). [CrossRef]

]. In medicine, UV radiation detection is also used in the treatment of certain diseases by phototherapy or in the investigation of photobiological effects [2

2. H. Oliver and H. Moseley, “The use of diode array spectroradiometers for dosimetry in phototherapy,” Phys. Med. Biol. 47(24), 4411–4421 (2002). [CrossRef]

]. For high performance detectors in the above applications, we need to consider their reliability, light weight, low operation voltage, and sensitivity to very weak signals. In particular, it would be advantageous to have detectors with high sensitivity to the UV but no response to visible light, because the UV radiation from the sun or other UV radiative sources needs to be measured without interference from the visible light.

2. Experiment

3. Results and discussion

3.1 The absorption spectra

Figure 2
Fig. 2 UV-visible absorption spectra of NPB (dash-dotted curve), PBD (dashed curve) and the NPB/PBD device (solid curve).
shows the absorption spectra of two 60-nm-thick NPB and PBD thin films deposited on quartz substrates, respectively, as well as the absorption spectra of the NPB/PBD device deposited on an ITO glass substrate. The absorption of the NPB thin film is in the range of 300–420 nm with its peak located at 350 nm, while for the PBD film there is stronger absorption in the UV region below 325 nm. The absorption spectrum of the device mainly corresponds to the absorption of the NPB thin film in the UV region above 325 nm. However, the bandgap of PBD is wider than NPB so that its contribution is greater in the region below 325 nm. Additionally, there is an almost negligible absorption of the ITO glass substrate in the region above 310 nm as compared with a strong absorption below 310 nm.

3.2 The J-V characteristic curves

The J-V characteristic curves of the NPB/PBD heterojunction diode measured in the dark and under 60 μW/cm2 of 350 nm light are plotted in Fig. 3
Fig. 3 Dark current (solid square) and photocurrent (vacant circle) vs. voltage for the device illuminated by a 60 μW/cm2 UV light at 350 nm.
. The extremely low value of the dark current shows the marked rectifying effect of the pn junction. For example, the dark current density of the device at −3 V and +3 V are 0.032 μA/cm2 and 0.011 μA/cm2, respectively, indicating a low background noise, while the photocurrent densities are 42.4 μA/cm2 and 267.8 μA/cm2, corresponding to a high SNR of more than 103 and 104. The figure shows that the device has a short circuit current density (J sc) of 7.7 μA/cm2, an open-circuit voltage (V oc) of 1.65 V, and a fill factor of 0.23.

3.3 The general mechanism

It can be seen that the forward bias photocurrent rises prominently with the external electric field, much more than in the reverse bias case. The general mechanism may be like this: after incident photons are absorbed, holes and electrons are simultaneously created in the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the donor and acceptor, respectively, then they quickly form photo-generated excitons by Coulomb attraction. These excitons then diffuse to the interface and dissociate into separate electrons and holes. Some of the free carriers recombine again and others transport through the donor or acceptor to their respective electrodes, driven by the potential between the electrodes (including the built-in field and the external field). Ultimately, only the carriers collected by the electrodes contribute to the photocurrent, and the interface of photo-generated exciton dissociation plays an important role in the generation of free carriers.

3.4 The photocurrent response

We also investigated the spectral response of the device based on a NPB/PBD heterojunction photodiode with different biases, as shown in Fig. 4
Fig. 4 Photocurrent spectral responses of the heterojunction device based on the ITO/NPB(80 nm)/PBD(40 nm)/LiF(1 nm)/Al(100 nm) structure at an applied potential of −3 V (dashed curve) and + 3 V (solid curve).
. A maximal response of about 4.5 A/W at 350 nm for the device operated at +3 V is obtained, which is nearly seven times larger than the response at −3 V. It is found that the photocurrent response curves of the device increase significantly between 300 and 420 nm under forward or reverse bias, which is basically consistent with the absorption spectra of the NPB donor. Since the incident light was incident from the ITO glass side and the NPB layer is thicker than the PBD layer, the main charges are generated in the former, which absorbs most of the incident light, and the lesser charges are generated in the latter by the residual light.

3.5 The quantum efficiency

The quantum efficiency η with a spectral range from 300 to 450 nm is shown in Fig. 5
Fig. 5 Quantum efficiency of the heterojunction device with semi-log curve at zero bias under 350 nm UV light.
, which is defined as the number of carriers generated per incident photon calculated by the equation of η = (|ISC|/qA) / (Pλ /) at V = 0V, where h is Plank’s constant and ν is the frequency of incident light; Pλ is the light power intensity; and A is the active area of the device for application. The quantum efficiency of the NPB/PBD hybrid device exhibits a nearly 3 order difference while illuminated under 380 nm and 450 nm light and the maximum value is 33%, indicating that the device can be used as a potentially cheap UV photodetector.

4. Conclusion

In summary, we have reported a high-response UV photodetector based on NPB and PBD. A low dark current density of 0.011 μA/cm2 and a large photocurrent density of 267.8 μA/cm2 at +3 V with a light intensity of 60 μW/cm2 at 350 nm were achieved. The high responsiveness of 4.5 A/W at +3 V compares very favorably with its inorganic counterparts based on GaN (150 mA/W) and SiC (120 mA/W) [14

14. Z. Su, W. Li, B. Chu, T. Li, J. Zhu, G. Zhang, F. Yan, X. Li, Y. Chen, and C. Lee, “High response organic ultraviolet photodetector based on blend of 4,4’,4”-tri-(2-methylphenyl phenylamino) triphenylaine and tris-(8-hydroxyquinoline) gallium,” Appl. Phys. Lett. 93(10), 103309 (2008). [CrossRef]

]. The transport mechanism of the charge carriers in the diode under forward and reverse bias is discussed. We believe this system can be a promising alternative for the fabrication of low-cost UV photodetectors.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (grants 50972007, 60476005, and 50532090), the Beijing Municipal Natural Science Foundation (grant 4092035), the Foundation of Beijing Jiaotong University (grant. 2006XZ008), the Special Items Fund of Beijing Municipal Commission of Education, and the National Science Fund for Distinguished Young Scholars (grant 60825407).

References and links

1.

M. Razeghi and A. Rogalski, “Semiconductor ultraviolet detectors,” J. Appl. Phys. 79(10), 7433 (1996). [CrossRef]

2.

H. Oliver and H. Moseley, “The use of diode array spectroradiometers for dosimetry in phototherapy,” Phys. Med. Biol. 47(24), 4411–4421 (2002). [CrossRef]

3.

J. Tuzzolino, “Silicon photodiode vacuum ultraviolet detector,” Rev. Sci. Instrum. 35(10), 1332 (1964). [CrossRef]

4.

R. D. Baertsch and J. R. Richardson, “An Ag-GaAs Schottky-barrier ultraviolet detector,” J. Appl. Phys. 40(1), 229 (1969). [CrossRef]

5.

Y. Zhou, C. Ahyi, C. Tin, J. Williams, M. Park, D. Kim, A. Cheng, D. Wang, A. Hanser, E. A. Preble, N. M. Williams, and K. Evans, “Fabrication and device characteristics of Schottky-type bulk GaN-based ‘visible-blind’ ultraviolet photodetectors,” Appl. Phys. Lett. 90(12), 121118 (2007). [CrossRef]

6.

J. Y. Duboz, J. L. Reverchon, D. Adam, B. Damilano, N. Grandjean, F. Semond, and J. Massies, “Submicron metal–semiconductor–metal ultraviolet detectors based on AlGaN grown on silicon: Results and simulation,” J. Appl. Phys. 92(9), 5602 (2002). [CrossRef]

7.

J. Li, Z. Y. Fan, R. Dahal, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang, “200 nm deep ultraviolet photodetectors based on AlN,” Appl. Phys. Lett. 89(21), 213510 (2006). [CrossRef]

8.

K. Wang, Y. Vygranenko, and A. Nathan, “ZnO-based p-i-n and n-i-p heterostructure ultraviolet sensors: a comparative study,” J. Appl. Phys. 101(11), 114508 (2007). [CrossRef]

9.

W. Yang, R. D. Vispute, S. Choopun, R. P. Sharma, T. Venkatesan, and H. Shen, “Ultraviolet photoconductive detector based on epitaxial Mg0.34Zn0.66O thin films,” Appl. Phys. Lett. 78(18), 2787 (2001). [CrossRef]

10.

X. Chen, H. Zhu, J. Cai, and Z. Wu, “High-performance 4H-SiC-based ultraviolet p-i-n photodetector,” J. Appl. Phys. 102(2), 024505 (2007). [CrossRef]

11.

F. Sciuto, F. Roccaforte, and V. Raineri, “Electro-optical response of ion-irradiated 4H-SiC Schottky ultraviolet photodetectors,” Appl. Phys. Lett. 92(9), 093505 (2008). [CrossRef]

12.

M. Liao, Y. Koide, and J. Alvarez, “Photovoltaic Schottky ultraviolet detectors fabricated on boron-doped homoepitaxial diamond layer,” Appl. Phys. Lett. 88(3), 033504 (2006). [CrossRef]

13.

D. Ray and K. L. Narasimhan, “High response organic visible-blind ultraviolet detector,” Appl. Phys. Lett. 91(9), 093516 (2007). [CrossRef]

14.

Z. Su, W. Li, B. Chu, T. Li, J. Zhu, G. Zhang, F. Yan, X. Li, Y. Chen, and C. Lee, “High response organic ultraviolet photodetector based on blend of 4,4’,4”-tri-(2-methylphenyl phenylamino) triphenylaine and tris-(8-hydroxyquinoline) gallium,” Appl. Phys. Lett. 93(10), 103309 (2008). [CrossRef]

15.

S. C. Tse, K. C. Kwok, and S. K. So, “Electron transport in naphthylamine-based organic compounds,” Appl. Phys. Lett. 89(26), 262102 (2006). [CrossRef]

16.

S. C. Tse, S. W. Tsang, and S. K. So, “Polymeric conducting anode for small organic transporting molecules in dark injection experiments,” J. Appl. Phys. 100(6), 063708 (2006). [CrossRef]

17.

H. Choukri, A. Fischer, S. Forget, S. Chénais, M. Castex, D. Adès, A. Siove, and B. Geffroy, “White organic light-emitting diodes with fine chromaticity tuning via ultrathin layer position shifting,” Appl. Phys. Lett. 89(18), 183513 (2006). [CrossRef]

18.

S. C. Tse, K. K. Tsung, and S. K. So, “Single-layer organic light-emitting diodes using naphthyl diamine,” Appl. Phys. Lett. 90(21), 213502 (2007). [CrossRef]

19.

S. Chang, G. He, F. Chen, T. Guo, and Y. Yang, “Degradation mechanism of phosphorescent-dye-doped polymer light-emitting diodes,” Appl. Phys. Lett. 79(13), 2088 (2001). [CrossRef]

20.

R. Schlaf, B. A. Parkinson, P. A. Lee, K. W. Nebesny, G. Jabbour, B. Kippelen, N. Peyghambarian, and N. R. Armstrong, “Photoemission spectroscopy of LiF coated Al and Pt electrodes,” J. Appl. Phys. 84(12), 6729 (1998). [CrossRef]

21.

S. D. Wang, M. K. Fung, S. L. Lai, S. W. Tong, C. S. Lee, S. T. Lee, H. J. Zhang, and S. N. Bao, “Experimental study of a chemical reaction between LiF and Al,” J. Appl. Phys. 94(1), 169 (2003). [CrossRef]

22.

R. Schroeder and B. Ullrich, “Photovoltaic hybrid device with broad tunable spectral response achieved by organic/inorganic thin-film heteropairing,” Appl. Phys. Lett. 81(3), 556 (2002). [CrossRef]

OCIS Codes
(040.5160) Detectors : Photodetectors
(040.7190) Detectors : Ultraviolet
(160.4890) Materials : Organic materials

ToC Category:
Detectors

History
Original Manuscript: September 10, 2009
Revised Manuscript: January 29, 2010
Manuscript Accepted: February 12, 2010
Published: May 19, 2010

Citation
Q. Dai and X. Q. Zhang, "High-response ultraviolet photodetector based on N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine and 2-(4-tertbutylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole," Opt. Express 18, 11821-11826 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-11-11821


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References

  1. M. Razeghi and A. Rogalski, “Semiconductor ultraviolet detectors,” J. Appl. Phys. 79(10), 7433 (1996). [CrossRef]
  2. H. Oliver and H. Moseley, “The use of diode array spectroradiometers for dosimetry in phototherapy,” Phys. Med. Biol. 47(24), 4411–4421 (2002). [CrossRef]
  3. J. Tuzzolino, “Silicon photodiode vacuum ultraviolet detector,” Rev. Sci. Instrum. 35(10), 1332 (1964). [CrossRef]
  4. R. D. Baertsch and J. R. Richardson, “An Ag-GaAs Schottky-barrier ultraviolet detector,” J. Appl. Phys. 40(1), 229 (1969). [CrossRef]
  5. Y. Zhou, C. Ahyi, C. Tin, J. Williams, M. Park, D. Kim, A. Cheng, D. Wang, A. Hanser, E. A. Preble, N. M. Williams, and K. Evans, “Fabrication and device characteristics of Schottky-type bulk GaN-based ‘visible-blind’ ultraviolet photodetectors,” Appl. Phys. Lett. 90(12), 121118 (2007). [CrossRef]
  6. J. Y. Duboz, J. L. Reverchon, D. Adam, B. Damilano, N. Grandjean, F. Semond, and J. Massies, “Submicron metal–semiconductor–metal ultraviolet detectors based on AlGaN grown on silicon: Results and simulation,” J. Appl. Phys. 92(9), 5602 (2002). [CrossRef]
  7. J. Li, Z. Y. Fan, R. Dahal, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang, “200 nm deep ultraviolet photodetectors based on AlN,” Appl. Phys. Lett. 89(21), 213510 (2006). [CrossRef]
  8. K. Wang, Y. Vygranenko, and A. Nathan, “ZnO-based p-i-n and n-i-p heterostructure ultraviolet sensors: a comparative study,” J. Appl. Phys. 101(11), 114508 (2007). [CrossRef]
  9. W. Yang, R. D. Vispute, S. Choopun, R. P. Sharma, T. Venkatesan, and H. Shen, “Ultraviolet photoconductive detector based on epitaxial Mg0.34Zn0.66O thin films,” Appl. Phys. Lett. 78(18), 2787 (2001). [CrossRef]
  10. X. Chen, H. Zhu, J. Cai, and Z. Wu, “High-performance 4H-SiC-based ultraviolet p-i-n photodetector,” J. Appl. Phys. 102(2), 024505 (2007). [CrossRef]
  11. F. Sciuto, F. Roccaforte, and V. Raineri, “Electro-optical response of ion-irradiated 4H-SiC Schottky ultraviolet photodetectors,” Appl. Phys. Lett. 92(9), 093505 (2008). [CrossRef]
  12. M. Liao, Y. Koide, and J. Alvarez, “Photovoltaic Schottky ultraviolet detectors fabricated on boron-doped homoepitaxial diamond layer,” Appl. Phys. Lett. 88(3), 033504 (2006). [CrossRef]
  13. D. Ray and K. L. Narasimhan, “High response organic visible-blind ultraviolet detector,” Appl. Phys. Lett. 91(9), 093516 (2007). [CrossRef]
  14. Z. Su, W. Li, B. Chu, T. Li, J. Zhu, G. Zhang, F. Yan, X. Li, Y. Chen, and C. Lee, “High response organic ultraviolet photodetector based on blend of 4,4’,4”-tri-(2-methylphenyl phenylamino) triphenylaine and tris-(8-hydroxyquinoline) gallium,” Appl. Phys. Lett. 93(10), 103309 (2008). [CrossRef]
  15. S. C. Tse, K. C. Kwok, and S. K. So, “Electron transport in naphthylamine-based organic compounds,” Appl. Phys. Lett. 89(26), 262102 (2006). [CrossRef]
  16. S. C. Tse, S. W. Tsang, and S. K. So, “Polymeric conducting anode for small organic transporting molecules in dark injection experiments,” J. Appl. Phys. 100(6), 063708 (2006). [CrossRef]
  17. H. Choukri, A. Fischer, S. Forget, S. Chénais, M. Castex, D. Adès, A. Siove, and B. Geffroy, “White organic light-emitting diodes with fine chromaticity tuning via ultrathin layer position shifting,” Appl. Phys. Lett. 89(18), 183513 (2006). [CrossRef]
  18. S. C. Tse, K. K. Tsung, and S. K. So, “Single-layer organic light-emitting diodes using naphthyl diamine,” Appl. Phys. Lett. 90(21), 213502 (2007). [CrossRef]
  19. S. Chang, G. He, F. Chen, T. Guo, and Y. Yang, “Degradation mechanism of phosphorescent-dye-doped polymer light-emitting diodes,” Appl. Phys. Lett. 79(13), 2088 (2001). [CrossRef]
  20. R. Schlaf, B. A. Parkinson, P. A. Lee, K. W. Nebesny, G. Jabbour, B. Kippelen, N. Peyghambarian, and N. R. Armstrong, “Photoemission spectroscopy of LiF coated Al and Pt electrodes,” J. Appl. Phys. 84(12), 6729 (1998). [CrossRef]
  21. S. D. Wang, M. K. Fung, S. L. Lai, S. W. Tong, C. S. Lee, S. T. Lee, H. J. Zhang, and S. N. Bao, “Experimental study of a chemical reaction between LiF and Al,” J. Appl. Phys. 94(1), 169 (2003). [CrossRef]
  22. R. Schroeder and B. Ullrich, “Photovoltaic hybrid device with broad tunable spectral response achieved by organic/inorganic thin-film heteropairing,” Appl. Phys. Lett. 81(3), 556 (2002). [CrossRef]

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