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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 13 — Jul. 1, 2013
  • pp: 15676–15685
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A PN-type quantum barrier for InGaN/GaN light emitting diodes

Zi-Hui Zhang, Swee Tiam Tan, Yun Ji, Wei Liu, Zhengang Ju, Zabu Kyaw, Xiao Wei Sun, and Hilmi Volkan Demir  »View Author Affiliations


Optics Express, Vol. 21, Issue 13, pp. 15676-15685 (2013)
http://dx.doi.org/10.1364/OE.21.015676


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Abstract

In this work, InGaN/GaN light-emitting diodes (LEDs) with PN-type quantum barriers are comparatively studied both theoretically and experimentally. A strong enhancement in the optical output power is obtained from the proposed device. The improved performance is attributed to the screening of the quantum confined Stark effect (QCSE) in the quantum wells and improved hole transport across the active region. In addition, the enhanced overall radiative recombination rates in the multiple quantum wells and increased effective energy barrier height in the conduction band has substantially suppressed the electron leakage from the active region. Furthermore, the electrical conductivity in the proposed devices is improved. The numerical and experimental results are in excellent agreement and indicate that the PN-type quantum barriers hold great promise for high-performance InGaN/GaN LEDs.

© 2013 OSA

1. Introduction

P-type GaN is a milestone in the development of InGaN light-emitting diodes (LEDs), since the issues of p-type GaN have been solved [1

1. S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa, “Thermal annealing effects on p-type Mg-doped GaN films,” Jpn. J. Appl. Phys. 31(Part 2, No. 2B2B), 139–142 (1992). [CrossRef]

, 2

2. H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, “P-type conduction in Mg-doped GaN treated with low-energy electron-beam irradiation (LEEBI),” Jpn. J. Appl. Phys. 28(12), L2112–L2114 (1989). [CrossRef]

]. InGaN/GaN LEDs have made tremendous progress in the past decades, and they are now regarded as the new-generation light-emitting sources to replace the traditional lamps [3

3. S. T. Tan, X. W. Sun, H. V. Demir, and S. P. DenBaars, “Advances in the LED materials and architectures for energy-saving solid-state lighting toward “lighting revolution”,” IEEE Photon. J. 4(2), 613–619 (2012). [CrossRef]

5

5. N. Tansu, H. Zhao, G. Liu, X. H. Li, J. Zhang, H. Tong, and Y. K. Ee, “III-nitride photonics,” IEEE Photon. J. 2(2), 241–248 (2010). [CrossRef]

]. However, due to the heavy effective mass and low mobility, a poor transport of holes is identified to be responsible for the undesired hole accumulation in the quantum well close to the p-GaN side, and thus significantly limits the device performance. In order to improve the hole transport in the active region, InGaN quantum barriers with a graded InN fraction was previously proposed to homogenize the hole distribution [6

6. C. H. Wang, S. P. Chang, P. H. Ku, J. C. Li, Y. P. Lan, C. C. Lin, H. C. Yang, H. C. Kuo, T. C. Lu, S. C. Wang, and C. Y. Chang, “Hole transport improvement in InGaN/GaN light-emitting diodes by graded-composition multiple quantum barriers,” Appl. Phys. Lett. 99(17), 171106 (2011). [CrossRef]

]. Besides, selectively Mg-doped quantum barriers were found to facilitate the hole transport in the active region both numerically [7

7. M. C. Tsai, S. H. Yen, and Y. K. Kuo, “Carrier transportation and internal quantum efficiency of blue inGaN light-emitting diodes with p-doped barriers,” IEEE Photon. Technol. Lett. 22(6), 374–376 (2010). [CrossRef]

] and experimentally [8

8. S. J. Park, S. H. Han, C. Y. Cho, S. J. Lee, T. Y. Park, T. H. Kim, S. H. Park, S. Won Kang, J. Won Kim, and Y. C. Kim, “Effect of Mg doping in the barrier of InGaN/GaN multiple quantum well on optical power of light-emitting diodes,” Appl. Phys. Lett. 96(5), 051113 (2010). [CrossRef]

]. A thinner quantum barrier proves effective in homogenizing the hole distribution [9

9. M.-C. Tsai, S.-H. Yen, Y.-C. Lu, and Y.-K. Kuo, “Numerical study of blue InGaN light-emitting diodes with varied barrier thicknesses,” IEEE Photon. Technol. Lett. 23(2), 76–78 (2011). [CrossRef]

], but the electrons may fly over the thin quantum barriers without recombining with the holes. Thus, in addition to enhancing the hole transport, it is also essential to enhance the electron confinement by properly designing the electron blocking layer (EBL) and the quantum barriers, such as those based on the polarization matched AlGaInN used as EBL [10

10. M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, “Origin of efficiency droop in GaN-based light-emitting diodes,” Appl. Phys. Lett. 91(18), 183507 (2007). [CrossRef]

, 11

11. S. Choi, M.-H. Ji, J. Kim, H. J. Kim, M. M. Satter, P. D. Yoder, J.-H. Ryou, R. D. Dupuis, A. M. Fischer, and F. A. Ponce, “Efficiency droop due to electron spill-over and limited hole injection in III-nitride visible light-emitting diodes employing lattice-matched InAlN electron blocking layers,” Appl. Phys. Lett. 101(16), 161110 (2012). [CrossRef]

] and thin AlGaN or InAlN used as the cap layer for the quantum barriers [12

12. H. P. Zhao, G. Y. Liu, R. A. Arif, and N. Tansu, “Current injection efficiency induced efficiency-droop in InGaN quantum well light-emitting diodes,” Solid-State Electron. 54(10), 1119–1124 (2010). [CrossRef]

14

14. H. Zhao, G. Liu, J. Zhang, R. A. Arif, and N. Tansu, “Analysis of internal quantum efficiency and current injection efficiency in III-nitride light-emitting diodes,” J. Display Technol. 9(4), 212–225 (2013). [CrossRef]

].

2. Experiments

To verify the theoretical results, InGaN/GaN LED chips were fabricated by a standard fabrication process. The LED mesa (with a chip size of 350 × 350 μm2) was obtained by reactive ion etch (RIE). Ni/Au (5 nm/5 nm) was deposited by E-beam as the transparent current spreading layer (TCL) on the p-GaN layer. Ti/Au (30 nm/150 nm) was finally deposited on the n-GaN layer and TCL simultaneously for metal contacts.

3. Results and discussion

Figures 2(a)
Fig. 2 Experimentally measured EL spectra for (a) Device I, (b) Device II and (c) Device III at 16, 32, 48, 64 and 80 A/cm2, respectively.
, 2(b) and 2(c) show the experimentally measured electroluminescence (EL) spectra at various current density levels for Devices I, II and III, respectively. Among the three devices, the strongest EL intensity is observed from Device III with the PN-type quantum barriers. The strong EL intensity is attributed to the improved hole transport across the active region with the introduction of Mg dopants. In addition, the screening of the QCSE by Si step-doping the quantum barriers has also increased the radiative recombination rates in the quantum wells, resulting in a better device performance.

Figures 4(a)
Fig. 4 Calculated energy band diagrams for (a) Device I, (b) Device II and (c) Device III at 40 A/cm2, along with the effective conduction band barrier height (ΔΦe) and the effective valance band barrier height (ΔΦh).
, 4(b) and 4(c) show the calculated energy band diagrams for Devices I, II and III at 40 A/cm2, respectively. It is clearly shown that Device I has the smallest energy barrier height for holes [Fig. 4(a)]. The effective valance band barrier heights (ΔΦh) are 840, 716, 625 and 545 meV, respectively, as shown in Fig. 4(a). However, once the quantum barriers are step-doped with Si in Device II [see Fig. 4(b)], the effective valance band barrier heights are increased to 875, 755, 655 and 567 meV, respectively. Although the step-doped quantum barrier with Si dopants is effective in screening the QCSE [25

25. Z.-H. Zhang, S. T. Tan, Z. G. Ju, W. Liu, Y. Ji, Z. Kyaw, Y. Dikme, X. W. Sun, and H. V. Demir, “On the effect of step-doped quantum barriers in InGaN/GaN light emitting diodes,” J. Display Technol. 9(4), 226–233 (2013). [CrossRef]

], the increase in its valance band barrier height blocks the hole injection into the quantum wells away from the p-GaN layer, and this may limit the device performance. Fortunately, the hole blocking effect can be relieved in the PN-type quantum barriers through the introduction of Mg dopants [see Device III in Fig. 4(c)]. Therefore, the effective valence band barrier heights in the LED with PN-type quantum barriers are reduced to 845, 719, 627 and 550 meV, respectively.

In order to reveal the hole transport for Devices I, II and III with various quantum barrier schemes, we have further simulated the hole distribution across the quantum wells, as shown in Fig. 5(a)
Fig. 5 Simulated (a) hole concentration and (b) the radiative recombination rates for Devices I, II and III, respectively.
. Comparatively, we can see that Device I shows the most homogenous hole distribution across the active region because of the undoped GaN quantum barriers. On the other hand, for Device II, the holes have difficulty to penetrate across the active region due to its increased valence band barrier heights. As for Device III, since the valance band barrier heights are reduced through introducing Mg in the quantum barriers, holes are better distributed compared to Device II. However, since the ionized Mg in the quantum barriers is assumed to be 1 × 1017 cm−3 in our simulation, which is still smaller than the Si doping concentration, thus the valance band barrier height in Device III is still larger than that in Device I, and we still observe a less homogenous hole distribution if compared to Device I. Nevertheless, one can also properly reduce the quantum barrier thickness of Device III for an even better hole transport. Separately, we have examined the radiative recombination rates in each quantum well for Devices I, II and III numerically, as shown in Fig. 5(b). Although Devices I, II and III have the identical hole concentration in the quantum well that is closest to the p-GaN layer, the excellent screening of the QCSE with the Si-doped quantum barriers facilitates the strongest radiative recombination rates in the last quantum well for both Devices II and III [25

25. Z.-H. Zhang, S. T. Tan, Z. G. Ju, W. Liu, Y. Ji, Z. Kyaw, Y. Dikme, X. W. Sun, and H. V. Demir, “On the effect of step-doped quantum barriers in InGaN/GaN light emitting diodes,” J. Display Technol. 9(4), 226–233 (2013). [CrossRef]

]. Therefore, the enhanced overall radiative recombination rates and optical output power have been obtained in Figs. 3(a) and 3(b), respectively. For the rest of the quantum wells that are away from the p-GaN layer, Device III has the better radiative recombination rates compared to Device II due to the reduced valance band barrier height by selectively doping Mg in the quantum barriers, and this translates to the strongest optical output power for Device III according to Figs. 3(a) and 3(b), respectively.

The leakage current is shown in Fig. 6
Fig. 6 Simulated leakage current for Devices I, II and III, respectively.
. We have seen that the leakage current is 62.9%, 61.0% and 56.4% for Devices I, II and III, respectively. The suppressed leakage current in Devices II and III compared to Device I is attributed to the increased overall radiative recombination rates in the active region [see Fig. 5(b)] [30

30. J. Piprek, “Efficiency droop in nitride-based light-emitting diodes,” Phys. Status Solid. A-Appl. Mater. Sci. 207(10), 2217–2225 (2010).

]. On the other hand, by introducing Mg dopants in the quantum barriers, the effective conduction band barrier height (ΔΦe) can be increased for Device III when compared to Device II [see ΔΦein Figs. 4(b) and 4(c)]. Thus, an even better electron confinement in Device III is obtained once the effective conduction band barrier height is increased [10

10. M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, “Origin of efficiency droop in GaN-based light-emitting diodes,” Appl. Phys. Lett. 91(18), 183507 (2007). [CrossRef]

, 12

12. H. P. Zhao, G. Y. Liu, R. A. Arif, and N. Tansu, “Current injection efficiency induced efficiency-droop in InGaN quantum well light-emitting diodes,” Solid-State Electron. 54(10), 1119–1124 (2010). [CrossRef]

], and this can further reduce the electron leakage current according to Fig. 6.

The measured and simulated current as a function of the applied bias for the LED chips are demonstrated in Figs. 7(a)
Fig. 7 (a) Experimentally measured and (b) simulated current as a function of the applied voltage for Devices I, II and III, respectively.
and 7(b), respectively. It can be seen from Figs. 7(a) and 7(b) that Devices II and III exhibit a substantial improvement in their electrical performance compared to Device I. The enhanced on-state current is due to the improved electron transport in Devices II and III both with Si-doped quantum barriers. The Mg-doping in the quantum barriers for Device III also helps to enhance the hole injection and thus Device III has a slightly better electrical performance than Device II both from experiment and simulation. Furthermore, the strong radiative recombination current helps for a better electrical conductivity.

Besides, it is noteworthy that we have utilized four PN-type quantum barriers in this work, however, the number of PN-type quantum barriers and the Mg-doped position in each quantum barrier can be further optimized. By doing so, the possible Mg diffusion from the PN-type quantum barriers into the quantum wells can be further suppressed. Meanwhile, considering the compensation effect to the Si-doped position by those diffused Mg dopants in each quantum barrier, the Si dosage and Si-doped thickness can also be properly increased.

4. Conclusions

Acknowledgments

This work is supported by the National Research Foundation of Singapore under Grant No. NRF-CRP-6-2010-2 and NRF-RF-2009-09 and the Singapore Agency for Science, Technology and Research (A*STAR) SERC under Grant No. 112 120 2009. The work is also supported by the National Natural Science Foundation of China (NSFC) (Project Nos. 61006037, 61177014 and 61076015).

References and links

1.

S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa, “Thermal annealing effects on p-type Mg-doped GaN films,” Jpn. J. Appl. Phys. 31(Part 2, No. 2B2B), 139–142 (1992). [CrossRef]

2.

H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, “P-type conduction in Mg-doped GaN treated with low-energy electron-beam irradiation (LEEBI),” Jpn. J. Appl. Phys. 28(12), L2112–L2114 (1989). [CrossRef]

3.

S. T. Tan, X. W. Sun, H. V. Demir, and S. P. DenBaars, “Advances in the LED materials and architectures for energy-saving solid-state lighting toward “lighting revolution”,” IEEE Photon. J. 4(2), 613–619 (2012). [CrossRef]

4.

M. H. Crawford, “LEDs for solid-state lighting: performance challenges and recent advances,” IEEE J. Sel. Top. Quantum Electron. 15(4), 1028–1040 (2009). [CrossRef]

5.

N. Tansu, H. Zhao, G. Liu, X. H. Li, J. Zhang, H. Tong, and Y. K. Ee, “III-nitride photonics,” IEEE Photon. J. 2(2), 241–248 (2010). [CrossRef]

6.

C. H. Wang, S. P. Chang, P. H. Ku, J. C. Li, Y. P. Lan, C. C. Lin, H. C. Yang, H. C. Kuo, T. C. Lu, S. C. Wang, and C. Y. Chang, “Hole transport improvement in InGaN/GaN light-emitting diodes by graded-composition multiple quantum barriers,” Appl. Phys. Lett. 99(17), 171106 (2011). [CrossRef]

7.

M. C. Tsai, S. H. Yen, and Y. K. Kuo, “Carrier transportation and internal quantum efficiency of blue inGaN light-emitting diodes with p-doped barriers,” IEEE Photon. Technol. Lett. 22(6), 374–376 (2010). [CrossRef]

8.

S. J. Park, S. H. Han, C. Y. Cho, S. J. Lee, T. Y. Park, T. H. Kim, S. H. Park, S. Won Kang, J. Won Kim, and Y. C. Kim, “Effect of Mg doping in the barrier of InGaN/GaN multiple quantum well on optical power of light-emitting diodes,” Appl. Phys. Lett. 96(5), 051113 (2010). [CrossRef]

9.

M.-C. Tsai, S.-H. Yen, Y.-C. Lu, and Y.-K. Kuo, “Numerical study of blue InGaN light-emitting diodes with varied barrier thicknesses,” IEEE Photon. Technol. Lett. 23(2), 76–78 (2011). [CrossRef]

10.

M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, “Origin of efficiency droop in GaN-based light-emitting diodes,” Appl. Phys. Lett. 91(18), 183507 (2007). [CrossRef]

11.

S. Choi, M.-H. Ji, J. Kim, H. J. Kim, M. M. Satter, P. D. Yoder, J.-H. Ryou, R. D. Dupuis, A. M. Fischer, and F. A. Ponce, “Efficiency droop due to electron spill-over and limited hole injection in III-nitride visible light-emitting diodes employing lattice-matched InAlN electron blocking layers,” Appl. Phys. Lett. 101(16), 161110 (2012). [CrossRef]

12.

H. P. Zhao, G. Y. Liu, R. A. Arif, and N. Tansu, “Current injection efficiency induced efficiency-droop in InGaN quantum well light-emitting diodes,” Solid-State Electron. 54(10), 1119–1124 (2010). [CrossRef]

13.

G. Liu, J. Zhang, C. K. Tan, and N. Tansu, “Efficiency-droop suppression by using large-bandgap AlGaInN thin barrier layers in InGaN quantum-well light-emitting diodes,” IEEE Photon. J. 5(2), 220101 (2013). [CrossRef]

14.

H. Zhao, G. Liu, J. Zhang, R. A. Arif, and N. Tansu, “Analysis of internal quantum efficiency and current injection efficiency in III-nitride light-emitting diodes,” J. Display Technol. 9(4), 212–225 (2013). [CrossRef]

15.

S.-H. Park and S.-L. Chuang, “Comparison of zinc-blende and wurtzite GaN semiconductors with spontaneous polarization and piezoelectric field effects,” J. Appl. Phys. 87(1), 353–364 (2000). [CrossRef]

16.

R. A. Arif, Y.-K. Ee, and N. Tansu, “Polarization engineering via staggered InGaN quantum wells for radiative efficiency enhancement of light emitting diodes,” Appl. Phys. Lett. 91(9), 091110 (2007). [CrossRef]

17.

J.-H. Ryou, P. D. Yoder, J. Liu, Z. Lochner, K. Hyunsoo, S. Choi, H.-J. Kim, and R. D. Dupuis, “Control of quantum-confined Stark effect in InGaN-based quantum wells,” IEEE J. Sel. Top. Quantum Electron. 15(4), 1080–1091 (2009). [CrossRef]

18.

H. Zhao, G. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, and N. Tansu, “Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells,” Opt. Express 19(S4Suppl 4), A991–A1007 (2011). [CrossRef] [PubMed]

19.

S. H. Park, D. Ahn, B. H. Koo, and J. E. Oh, “Optical gain improvement in type-II InGaN/GaNSb/GaN quantum well structures composed of InGaN/and GaNSb layers,” Appl. Phys. Lett. 96(5), 051106 (2010). [CrossRef]

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R. A. Arif, H. Zhao, and N. Tansu, “Type-II InGaN-GaNAs quantum wells for lasers applications,” Appl. Phys. Lett. 92(1), 011104 (2008). [CrossRef]

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H. Zhao, R. A. Arif, and N. Tansu, “Self-consistent gain analysis of type-II `W' InGaN–GaNAs quantum well lasers,” J. Appl. Phys. 104(4), 043104 (2008). [CrossRef]

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J. Zhang and N. Tansu, “Improvement in spontaneous emission rates for InGaN quantum wells on ternary InGaN substrate for light-emitting diodes,” J. Appl. Phys. 110(11), 113110 (2011). [CrossRef]

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T. Deguchi, A. Shikanai, K. Torii, T. Sota, S. Chichibu, and S. Nakamura, “Luminescence spectra from InGaN multiquantum wells heavily doped with Si,” Appl. Phys. Lett. 72(25), 3329–3331 (1998). [CrossRef]

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J. H. Ryou, J. Limb, W. Lee, J. P. Liu, Z. Lochner, D. W. Yoo, and R. D. Dupuis, “Effect of silicon doping in the quantum-well barriers on the electrical and optical properties of visible green light-emitting diodes,” IEEE Photon. Technol. Lett. 20(21), 1769–1771 (2008). [CrossRef]

25.

Z.-H. Zhang, S. T. Tan, Z. G. Ju, W. Liu, Y. Ji, Z. Kyaw, Y. Dikme, X. W. Sun, and H. V. Demir, “On the effect of step-doped quantum barriers in InGaN/GaN light emitting diodes,” J. Display Technol. 9(4), 226–233 (2013). [CrossRef]

26.

Z. G. Ju, S. T. Tan, Z.-H. Zhang, Y. Ji, Z. Kyaw, Y. Dikme, X. W. Sun, and H. V. Demir, “On the origin of the redshift in the emission wavelength of InGaN/GaN blue light emitting diodes grown with a higher temperature interlayer,” Appl. Phys. Lett. 100(12), 123503 (2012). [CrossRef]

27.

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30.

J. Piprek, “Efficiency droop in nitride-based light-emitting diodes,” Phys. Status Solid. A-Appl. Mater. Sci. 207(10), 2217–2225 (2010).

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33.

M. Meneghini, N. Trivellin, G. Meneghesso, E. Zanoni, U. Zehnder, and B. Hahn, “A combined electro-optical method for the determination of the recombination parameters in InGaN-based light-emitting diodes,” J. Appl. Phys. 106(11), 114508 (2009). [CrossRef]

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35.

Z.-H. Zhang, S. T. Tan, W. Liu, Z. G. Ju, K. Zheng, Z. Kyaw, Y. Ji, N. Hasanov, X. W. Sun, and H. V. Demir, “Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-spreading layer,” Opt. Express 21(4), 4958–4969 (2013). [CrossRef] [PubMed]

OCIS Codes
(160.6000) Materials : Semiconductor materials
(230.3670) Optical devices : Light-emitting diodes
(230.5590) Optical devices : Quantum-well, -wire and -dot devices

ToC Category:
Optical Devices

History
Original Manuscript: April 2, 2013
Revised Manuscript: June 12, 2013
Manuscript Accepted: June 13, 2013
Published: June 24, 2013

Citation
Zi-Hui Zhang, Swee Tiam Tan, Yun Ji, Wei Liu, Zhengang Ju, Zabu Kyaw, Xiao Wei Sun, and Hilmi Volkan Demir, "A PN-type quantum barrier for InGaN/GaN light emitting diodes," Opt. Express 21, 15676-15685 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-13-15676


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References

  1. S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa, “Thermal annealing effects on p-type Mg-doped GaN films,” Jpn. J. Appl. Phys.31(Part 2, No. 2B2B), 139–142 (1992). [CrossRef]
  2. H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, “P-type conduction in Mg-doped GaN treated with low-energy electron-beam irradiation (LEEBI),” Jpn. J. Appl. Phys.28(12), L2112–L2114 (1989). [CrossRef]
  3. S. T. Tan, X. W. Sun, H. V. Demir, and S. P. DenBaars, “Advances in the LED materials and architectures for energy-saving solid-state lighting toward “lighting revolution”,” IEEE Photon. J.4(2), 613–619 (2012). [CrossRef]
  4. M. H. Crawford, “LEDs for solid-state lighting: performance challenges and recent advances,” IEEE J. Sel. Top. Quantum Electron.15(4), 1028–1040 (2009). [CrossRef]
  5. N. Tansu, H. Zhao, G. Liu, X. H. Li, J. Zhang, H. Tong, and Y. K. Ee, “III-nitride photonics,” IEEE Photon. J.2(2), 241–248 (2010). [CrossRef]
  6. C. H. Wang, S. P. Chang, P. H. Ku, J. C. Li, Y. P. Lan, C. C. Lin, H. C. Yang, H. C. Kuo, T. C. Lu, S. C. Wang, and C. Y. Chang, “Hole transport improvement in InGaN/GaN light-emitting diodes by graded-composition multiple quantum barriers,” Appl. Phys. Lett.99(17), 171106 (2011). [CrossRef]
  7. M. C. Tsai, S. H. Yen, and Y. K. Kuo, “Carrier transportation and internal quantum efficiency of blue inGaN light-emitting diodes with p-doped barriers,” IEEE Photon. Technol. Lett.22(6), 374–376 (2010). [CrossRef]
  8. S. J. Park, S. H. Han, C. Y. Cho, S. J. Lee, T. Y. Park, T. H. Kim, S. H. Park, S. Won Kang, J. Won Kim, and Y. C. Kim, “Effect of Mg doping in the barrier of InGaN/GaN multiple quantum well on optical power of light-emitting diodes,” Appl. Phys. Lett.96(5), 051113 (2010). [CrossRef]
  9. M.-C. Tsai, S.-H. Yen, Y.-C. Lu, and Y.-K. Kuo, “Numerical study of blue InGaN light-emitting diodes with varied barrier thicknesses,” IEEE Photon. Technol. Lett.23(2), 76–78 (2011). [CrossRef]
  10. M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, “Origin of efficiency droop in GaN-based light-emitting diodes,” Appl. Phys. Lett.91(18), 183507 (2007). [CrossRef]
  11. S. Choi, M.-H. Ji, J. Kim, H. J. Kim, M. M. Satter, P. D. Yoder, J.-H. Ryou, R. D. Dupuis, A. M. Fischer, and F. A. Ponce, “Efficiency droop due to electron spill-over and limited hole injection in III-nitride visible light-emitting diodes employing lattice-matched InAlN electron blocking layers,” Appl. Phys. Lett.101(16), 161110 (2012). [CrossRef]
  12. H. P. Zhao, G. Y. Liu, R. A. Arif, and N. Tansu, “Current injection efficiency induced efficiency-droop in InGaN quantum well light-emitting diodes,” Solid-State Electron.54(10), 1119–1124 (2010). [CrossRef]
  13. G. Liu, J. Zhang, C. K. Tan, and N. Tansu, “Efficiency-droop suppression by using large-bandgap AlGaInN thin barrier layers in InGaN quantum-well light-emitting diodes,” IEEE Photon. J.5(2), 220101 (2013). [CrossRef]
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