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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 25 — Dec. 7, 2009
  • pp: 22912–22917
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UV light emission from GZO/ZnO/GaN heterojunction diodes with carrier confinement layers

Min-Yung Ke, Tzu-Chun Lu, Sheng-Chieh Yang, Cheng-Pin Chen, Yun-Wei Cheng, Liang-Yi Chen, Cheng-Ying Chen, Jr-Hau He, and JianJang Huang  »View Author Affiliations


Optics Express, Vol. 17, Issue 25, pp. 22912-22917 (2009)
http://dx.doi.org/10.1364/OE.17.022912


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Abstract

In this work, GZO/ZnO/GaN diodes with the light emitting ZnO layer sandwiched between two SiO2 thin films was fabricated and characterized. We observed a strong excitonic emission at the wavelength 377nm with the Mg2+ deep level transition and oxygen vacancy induced recombination significantly suppressed. In comparison, light emission from the GZO/GaN device (without SiO2 barriers) is mainly dominant by defect radiation. Furthermore, the device with confinement layers demonstrated a much higher UV intensity than the blue-green emission of the GZO/GaN p-n device.

© 2009 OSA

1. Introduction

Recently, ultraviolet (UV) light-emitting diodes (LEDs) and laser diodes (LDs) have attracted much attention for applications to efficient solid state lighting, high-density information storage, and medical treatment. In addition to GaN, ZnO has been identified as a promising material for UV light sources due to its large exciton binding energy of 60 meV and the direct bandgap energy of 3.37 eV at room temperature. ZnO also offers several manufacturing advantages such as its compatibility with wet chemical etching, relatively low material cost, and long-term stability. Up to now, despite homojunction ZnO diodes have been reported [1

1. S. J. Jiao, Z. Z. Zhang, Y. M. Lu, D. Z. Shen, B. Yao, J. Y. Zhang, B. H. Li, D. X. Zhao, X. W. Fan, and Z. K. Tang, “ZnO p-n junction light-emitting diodes fabricated on sapphire substrates,” Appl. Phys. Lett. 88(3), 031911 ( 2006). [CrossRef]

,2

2. W. Liu, S. L. Gu, J. D. Ye, S. M. Zhu, S. M. Liu, X. Zhou, R. Zhang, Y. Shi, Y. D. Zheng, Y. Hang, and C. L. Zhang, “Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique,” Appl. Phys. Lett. 88(9), 092101 ( 2006). [CrossRef]

], difficulties in realizing reliable p-type ZnO have driven most ZnO based LEDs developed on heterostructures by growing n-ZnO on p-type semiconductors such as GaN, Si, AlGaN, and p-SrCu2O2 [3

3. J. Y. Lee, J. H. Lee, H. S. Kim, C. H. Lee, H. S. Ahn, H. K. Cho, Y. Y. Kim, B. H. Kong, and H. S. Lee, “A study on the origin of emission of the annealed n-ZnO/p-GaN heterostructure LED,” Thin Solid Films 517(17), 5157–5160 ( 2009). [CrossRef]

6

6. H. Ohta, K.-I. Kawamura, M. Orita, M. Hirano, N. Sarukura, and H. Hosono, “Current injection emission from a transparent p –n junction composed of p-SrCu2O2 /n-ZnO,” Appl. Phys. Lett. 77(4), 475 ( 2000). [CrossRef]

]. Among the p-type materials of choice, GaN is an excellent candidate as it is readily available and has the same wurtzite structure as ZnO. The n-ZnO/p-GaN based diode structures have been reported in the past several years with light emission ranging approximately between 370 and 600nm [3

3. J. Y. Lee, J. H. Lee, H. S. Kim, C. H. Lee, H. S. Ahn, H. K. Cho, Y. Y. Kim, B. H. Kong, and H. S. Lee, “A study on the origin of emission of the annealed n-ZnO/p-GaN heterostructure LED,” Thin Solid Films 517(17), 5157–5160 ( 2009). [CrossRef]

], [7

7. D. J. Rogers, F. Hosseini Teherani, A. Yasan, K. Minder, P. Kung, and M. Razeghi, “Electroluminescence at 375 nm from a ZnO/GaN:Mg/c-Al2O3 heterojunction light emitting diode,” Appl. Phys. Lett. 88(14), 141918 ( 2006). [CrossRef]

], [8

8. J. W. Sun, Y. M. Lu, Y. C. Liu, D. Z. Shen, Z. Z. Zhang, B. H. Li, J. Y. Zhang, B. Yao, D. X. Zhao, and X. W. Fan, “Excitonic electroluminescence from ZnO-based heterojunction light emitting diodes,” J. Phys. D Appl. Phys. 41(15), 155103 ( 2008). [CrossRef]

].

The variations of light emission from ZnO/GaN p-n heterostructures are attributed to several factors. First, radiative recombinations due to deep level defect recombination in p-GaN and oxygen vacancies in ZnO account for the emission at around 430nm and 530~550nm, respectively [9

9. M. A. Khan, Q. Chen, R. A. Skogman, and J. N. Kuznia, “Violet-blue GaN homojunction light emitting diodes with rapid thermal annealed p-type layers,” Appl. Phys. Lett. 66(16), 2046 ( 1995). [CrossRef]

12

12. H. S. Kang, J. S. Kang, J. W. Kim, and S. Y. Lee, “Annealing effect on the property of ultraviolet and green emissions of ZnO thin films,” J. Appl. Phys. 95(3), 1246 ( 2004). [CrossRef]

]. And light emission at the wavelength shorter than 430nm is associated with the ZnO excitonic recombination or band-to-band transition based on the band lineup calculations using the Thomson model [13

13. A. G. Milnes, and D. L. Feucht, “Heterojunctions and Metal-Semiconductor Junctions” (Academic, New York, 1972)

], which the emission wavelengh is determined by the location where electron and hole accumulate. In spite of these findings, most reported ZnO/GaN diodes employ a simple p-n or p-i-n heterostructures which the UV recombination efficiency is limited and a noticeable defect band radiation is generated.

To suppress light emission in the defect states and meanwhile enhance UV light emission from the ZnO band edge transition, in this work, we fabricate a ZnO light emitting layer sandwiched between two SiO2 confinement barriers of asymmetric thickness. The electrical and optical properties of the devices are characterized.

2. Device fabrication

3. Results and discussions

3.1 Photoluminescent spectra of ZnO and p-GaN

3.2 Electrical and optical properties of GZO/GaN and GZO/ZnO/GaN LEDs

The current-voltage curves in Fig. 2
Fig. 2 Current-voltage curves of a GZO/GaN LED (solid line) and a GZO/ZnO/GaN device with SiO2 confinement layers (dashed line).
indicate that both samples with and without SiO2 barriers demonstrate a nonlinear rectifying behavior. An additional voltage drop across the confinement layers is observed for the devices with SiO2 thin films.

4. Summary

Acknowledgments

This work was supported by the National Science Council of Taiwan under the grants NSC 97-2221-E-002-054-MY3.

References and links

1.

S. J. Jiao, Z. Z. Zhang, Y. M. Lu, D. Z. Shen, B. Yao, J. Y. Zhang, B. H. Li, D. X. Zhao, X. W. Fan, and Z. K. Tang, “ZnO p-n junction light-emitting diodes fabricated on sapphire substrates,” Appl. Phys. Lett. 88(3), 031911 ( 2006). [CrossRef]

2.

W. Liu, S. L. Gu, J. D. Ye, S. M. Zhu, S. M. Liu, X. Zhou, R. Zhang, Y. Shi, Y. D. Zheng, Y. Hang, and C. L. Zhang, “Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique,” Appl. Phys. Lett. 88(9), 092101 ( 2006). [CrossRef]

3.

J. Y. Lee, J. H. Lee, H. S. Kim, C. H. Lee, H. S. Ahn, H. K. Cho, Y. Y. Kim, B. H. Kong, and H. S. Lee, “A study on the origin of emission of the annealed n-ZnO/p-GaN heterostructure LED,” Thin Solid Films 517(17), 5157–5160 ( 2009). [CrossRef]

4.

J. D. Ye, S. L. Gu, S. M. Zhu, W. Liu, S. M. Liu, R. Zhang, Y. Shi, and Y. D. Zheng, “Electroluminescent and transport mechanisms of n-ZnO/p-Si heterojunctions,” Appl. Phys. Lett. 88(18), 182112 ( 2006). [CrossRef]

5.

Y. I. Alivov, E. V. Kalinina, A. E. Cherenkov, D. C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, and D. M. Bagnall, “Fabrication and characterization of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates,” Appl. Phys. Lett. 83(23), 4719 ( 2003). [CrossRef]

6.

H. Ohta, K.-I. Kawamura, M. Orita, M. Hirano, N. Sarukura, and H. Hosono, “Current injection emission from a transparent p –n junction composed of p-SrCu2O2 /n-ZnO,” Appl. Phys. Lett. 77(4), 475 ( 2000). [CrossRef]

7.

D. J. Rogers, F. Hosseini Teherani, A. Yasan, K. Minder, P. Kung, and M. Razeghi, “Electroluminescence at 375 nm from a ZnO/GaN:Mg/c-Al2O3 heterojunction light emitting diode,” Appl. Phys. Lett. 88(14), 141918 ( 2006). [CrossRef]

8.

J. W. Sun, Y. M. Lu, Y. C. Liu, D. Z. Shen, Z. Z. Zhang, B. H. Li, J. Y. Zhang, B. Yao, D. X. Zhao, and X. W. Fan, “Excitonic electroluminescence from ZnO-based heterojunction light emitting diodes,” J. Phys. D Appl. Phys. 41(15), 155103 ( 2008). [CrossRef]

9.

M. A. Khan, Q. Chen, R. A. Skogman, and J. N. Kuznia, “Violet-blue GaN homojunction light emitting diodes with rapid thermal annealed p-type layers,” Appl. Phys. Lett. 66(16), 2046 ( 1995). [CrossRef]

10.

R. W. Chuang, R. X. Wu, L. W. Lai, and C. T. Lee, “ZnO-on-GaN heterojunction light-emitting diode grown by vapor cooling condensation technique,” Appl. Phys. Lett. 91(23), 231113 ( 2007). [CrossRef]

11.

Y. Chen, D. M. Bagnall, H. J. Koh, K. T. Park, K. Hiraga, Z. Zhu, and T. Yao, “Plasma assisted molecular beam epitaxy of ZnO on c -plane sapphire: Growth and characterization,” J. Appl. Phys. 84(7), 3912 ( 1998). [CrossRef]

12.

H. S. Kang, J. S. Kang, J. W. Kim, and S. Y. Lee, “Annealing effect on the property of ultraviolet and green emissions of ZnO thin films,” J. Appl. Phys. 95(3), 1246 ( 2004). [CrossRef]

13.

A. G. Milnes, and D. L. Feucht, “Heterojunctions and Metal-Semiconductor Junctions” (Academic, New York, 1972)

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes

ToC Category:
Optical Devices

History
Original Manuscript: September 28, 2009
Revised Manuscript: November 9, 2009
Manuscript Accepted: November 23, 2009
Published: December 1, 2009

Citation
Min-Yung Ke, Tzu-Chun Lu, Sheng-Chieh Yang, Cheng-Pin Chen, Yun-Wei Cheng, Liang-Yi Chen, Cheng-Ying Chen, Jr-Hau He, and JianJang Huang, "UV light emission from GZO/ZnO/GaN heterojunction diodes with carrier confinement layers," Opt. Express 17, 22912-22917 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-25-22912


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References

  1. S. J. Jiao, Z. Z. Zhang, Y. M. Lu, D. Z. Shen, B. Yao, J. Y. Zhang, B. H. Li, D. X. Zhao, X. W. Fan, and Z. K. Tang, “ZnO p-n junction light-emitting diodes fabricated on sapphire substrates,” Appl. Phys. Lett. 88(3), 031911 (2006). [CrossRef]
  2. W. Liu, S. L. Gu, J. D. Ye, S. M. Zhu, S. M. Liu, X. Zhou, R. Zhang, Y. Shi, Y. D. Zheng, Y. Hang, and C. L. Zhang, “Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique,” Appl. Phys. Lett. 88(9), 092101 (2006). [CrossRef]
  3. J. Y. Lee, J. H. Lee, H. S. Kim, C. H. Lee, H. S. Ahn, H. K. Cho, Y. Y. Kim, B. H. Kong, and H. S. Lee, “A study on the origin of emission of the annealed n-ZnO/p-GaN heterostructure LED,” Thin Solid Films 517(17), 5157–5160 (2009). [CrossRef]
  4. J. D. Ye, S. L. Gu, S. M. Zhu, W. Liu, S. M. Liu, R. Zhang, Y. Shi, and Y. D. Zheng, “Electroluminescent and transport mechanisms of n-ZnO/p-Si heterojunctions,” Appl. Phys. Lett. 88(18), 182112 (2006). [CrossRef]
  5. Y. I. Alivov, E. V. Kalinina, A. E. Cherenkov, D. C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, and D. M. Bagnall, “Fabrication and characterization of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates,” Appl. Phys. Lett. 83(23), 4719 (2003). [CrossRef]
  6. H. Ohta, K.-I. Kawamura, M. Orita, M. Hirano, N. Sarukura, and H. Hosono, “Current injection emission from a transparent p –n junction composed of p-SrCu2O2 /n-ZnO,” Appl. Phys. Lett. 77(4), 475 (2000). [CrossRef]
  7. D. J. Rogers, F. Hosseini Teherani, A. Yasan, K. Minder, P. Kung, and M. Razeghi, “Electroluminescence at 375 nm from a ZnO/GaN:Mg/c-Al2O3 heterojunction light emitting diode,” Appl. Phys. Lett. 88(14), 141918 (2006). [CrossRef]
  8. J. W. Sun, Y. M. Lu, Y. C. Liu, D. Z. Shen, Z. Z. Zhang, B. H. Li, J. Y. Zhang, B. Yao, D. X. Zhao, and X. W. Fan, “Excitonic electroluminescence from ZnO-based heterojunction light emitting diodes,” J. Phys. D Appl. Phys. 41(15), 155103 (2008). [CrossRef]
  9. M. A. Khan, Q. Chen, R. A. Skogman, and J. N. Kuznia, “Violet-blue GaN homojunction light emitting diodes with rapid thermal annealed p-type layers,” Appl. Phys. Lett. 66(16), 2046 (1995). [CrossRef]
  10. R. W. Chuang, R. X. Wu, L. W. Lai, and C. T. Lee, “ZnO-on-GaN heterojunction light-emitting diode grown by vapor cooling condensation technique,” Appl. Phys. Lett. 91(23), 231113 (2007). [CrossRef]
  11. Y. Chen, D. M. Bagnall, H. J. Koh, K. T. Park, K. Hiraga, Z. Zhu, and T. Yao, “Plasma assisted molecular beam epitaxy of ZnO on c -plane sapphire: Growth and characterization,” J. Appl. Phys. 84(7), 3912 (1998). [CrossRef]
  12. H. S. Kang, J. S. Kang, J. W. Kim, and S. Y. Lee, “Annealing effect on the property of ultraviolet and green emissions of ZnO thin films,” J. Appl. Phys. 95(3), 1246 (2004). [CrossRef]
  13. A. G. Milnes, and D. L. Feucht, “Heterojunctions and Metal-Semiconductor Junctions” (Academic, New York, 1972)

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