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  • Editor: Christian Seassal
  • Vol. 22, Iss. S2 — Mar. 10, 2014
  • pp: A320–A327
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Optical properties of nanopillar AlGaN/GaN MQWs for ultraviolet light-emitting diodes

Peng Dong, Jianchang Yan, Yun Zhang, Junxi Wang, Chong Geng, Haiyang Zheng, Xuecheng Wei, Qingfeng Yan, and Jinmin Li  »View Author Affiliations


Optics Express, Vol. 22, Issue S2, pp. A320-A327 (2014)
http://dx.doi.org/10.1364/OE.22.00A320


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Abstract

Nanopillar AlGaN/GaN multiple quantum wells ultraviolet light-emitting diodes (LEDs) were fabricated by nanosphere lithography and dry-etching. The optical properties of the nanopillar LEDs were characterized by both temperature-dependent and time-resolved photoluminescence measurements. Compared to an as-grown sample, the nanopillar sample has a PL emission peak blue-shift of 7 meV, a 42% enhanced internal quantum efficiency at room temperature and a reduced radiative recombination lifetime from 870 picosecond to 621 picosecond at 7K. These results are directly from the suppressed quantum confined stark effect that is due to the strain relaxation in the nanopillar MQWs, further revealed by micro-Raman measurement. Additionally, finite-difference time domain simulation also proves better light extraction efficiency in the nanopillar LEDs.

© 2014 Optical Society of America

1. Introduction

AlGaN compound semiconductor has been widely explored for fabricating short-wavelength optoelectronic devices, such as ultraviolet (UV) light-emitting diodes (LEDs) [1

1. M. Asif Khan, M. Shatalov, H. P. Maruska, H. M. Wang, and E. Kuokstis, “III–Nitride UV Devices,” Jpn. J. Appl. Phys. 44(10), 7191–7206 (2005). [CrossRef]

] and laser diodes (LDs) [2

2. Z. Lochner, T.-T. Kao, Y.-S. Liu, X.-H. Li, M. Mahbub Satter, S.-C. Shen, P. Douglas Yoder, J.-H. Ryou, R. D. Dupuis, Y. Wei, H. Xie, A. Fischer, and F. A. Ponce, “Deep-ultraviolet lasing at 243 nm from photo-pumped AlGaN/AlN heterostructure on AlN substrate,” Appl. Phys. Lett. 102(10), 101110 (2013). [CrossRef]

] that are promising light sources for disinfection, bio-medical and UV curing, etc. However, strong piezoelectric field exists in AlGaN/(Al)GaN MQWs, leading to spatial separation of electrons and holes, or named the quantum confined stark effect (QCSE), which decreases the internal quantum efficiency (IQE) and brings a red-shift in emission spectrum [3

3. D. Miller, D. Chemla, T. Damen, A. Gossard, W. Wiegmann, T. Wood, and C. Burrus, “Band-Edge Electroabsorption in Quantum Well Structures: The Quantum-Confined Stark Effect,” Phys. Rev. Lett. 53(22), 2173–2176 (1984). [CrossRef]

, 4

4. J. S. Im, H. Kollmer, J. Off, A. Sohmer, F. Scholz, and A. Hangleiter, “Reduction of oscillator strength due to piezoelectric fields in GaN/AlxGa1-xN quantum wells,” Phys. Rev. B 57(16), R9435–R9438 (1998). [CrossRef]

]. Another issue is the low light extraction efficiency (LEE) of the AlGaN-based UV LED, which is caused by the internal total reflection at the epi-layers’ interfaces [5

5. Y. Y. Zhang, H. Z. Xie, H. Y. Zheng, T. B. Wei, H. Yang, J. Li, X. Y. Yi, X. Y. Song, G. H. Wang, and J. M. Li, “Light extraction efficiency improvement by multiple laser stealth dicing in InGaN-based blue light-emitting diodes,” Opt. Express 20(6), 6808–6815 (2012). [CrossRef] [PubMed]

, 6

6. A. Khan, K. Balakrishnan, and T. Katona, “Ultraviolet light-emitting diodes based on group three nitrides,” Nat. Photonics 2(2), 77–84 (2008). [CrossRef]

], as well as the UV absorption in the p-GaN layer commonly used on top of the p-AlGaN to enhance the hole injection [7

7. T. Nishida, N. Kobayashi, and T. Ban, “GaN-free transparent ultraviolet light-emitting diodes,” Appl. Phys. Lett. 82(1), 1 (2003). [CrossRef]

9

9. P. Dong, J. Yan, J. Wang, Y. Zhang, C. Geng, T. Wei, P. Cong, Y. Zhang, J. Zeng, Y. Tian, L. Sun, Q. Yan, J. Li, S. Fan, and Z. Qin, “282-nm AlGaN-based deep ultraviolet light-emitting diodes with improved performance on nano-patterned sapphire substrates,” Appl. Phys. Lett. 102(24), 241113 (2013). [CrossRef]

]. Although nanopillars and nanowires have been reported as effective structures to address the QCSE and low LEE issues in InGaN/GaN-based blue LEDs [10

10. J. Bai, Q. Wang, and T. Wang, “Characterization of InGaN-based nanorod light emitting diodes with different indium compositions,” J. Appl. Phys. 111(11), 113103 (2012). [CrossRef]

17

17. K. H. Li and H. W. Choi, “Air-spaced GaN nanopillar photonic band gap structures patterned by nanosphere lithography,” J. Appl. Phys. 109(2), 023107 (2011). [CrossRef]

], however, up to data the nanopillar structures have not been applied to AlGaN/GaN-based UV LEDs probably due to the difficulty to achieve high-quality AlGaN epitaxial materials, and nanopillars’ optical properties also have not been studied in depth yet.

In this paper, we fabricated nanopillar AlGaN/GaN LED arrays using nanosphere lithography (NSL) technique [17

17. K. H. Li and H. W. Choi, “Air-spaced GaN nanopillar photonic band gap structures patterned by nanosphere lithography,” J. Appl. Phys. 109(2), 023107 (2011). [CrossRef]

19

19. C. L. Cheung, R. J. Nikolic, C. E. Reinhardt, and T. F. Wang, “Fabrication of nanopillars by nanosphere lithography,” Nanotechnology 17(5), 1339–1343 (2006). [CrossRef]

] followed by a dry-etching process. Compared to other methods for fabricating nanopillar structures such as self-organized nickel islands [10

10. J. Bai, Q. Wang, and T. Wang, “Characterization of InGaN-based nanorod light emitting diodes with different indium compositions,” J. Appl. Phys. 111(11), 113103 (2012). [CrossRef]

], nano-imprinting [11

11. C. H. Liao, W. M. Chang, H. S. Chen, C. Y. Chen, Y. F. Yao, H. T. Chen, C. Y. Su, S. Y. Ting, Y. W. Kiang, and C. C. Yang, “Geometry and composition comparisons between c-plane disc-like and m-plane core-shell InGaN/GaN quantum wells in a nitride nanorod,” Opt. Express 20(14), 15859–15871 (2012). [CrossRef] [PubMed]

], electron-beam lithography [12

12. V. Ramesh, A. Kikuchi, K. Kishino, M. Funato, and Y. Kawakami, “Strain relaxation effect by nanotexturing InGaN/GaN multiple quantum well,” J. Appl. Phys. 107(11), 114303 (2010). [CrossRef]

] and interferometric lithography [20

20. S. D. Hersee, X. Y. Sun, and X. Wang, “The controlled growth of GaN nanowires,” Nano Lett. 6(8), 1808–1811 (2006). [CrossRef] [PubMed]

], NSL has advantages in cost, efficiency and large area uniformity. The optical properties of the nanopillar LEDs were investigated by cathodoluminescence (CL), temperature-dependent photoluminescence (PL) and time-resolved PL (TRPL) measurements, showing suppressed QCSE compared versus the as-grown LEDs. The strain relaxation within the nanopillar MQWs was confirmed by micro-Raman measurement. Besides, the finite difference time domain (FDTD) method was performed to simulate how the UV photons escape out of the LED device by comparing the LEE from top, bottom and side for both the as-grown and nanopillar samples.

2. Experiment

The AlGaN/GaN LED wafer was grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) on a 2-inch c-plane sapphire substrate. The LED structure consists a 25-nm-thick AlN nucleation layer grown at 550 °C, a 200-nm-thick AlN template layer grown at 1200 °C, 20 pairs of AlN/AlGaN superlattices (SLs), a 3-μm-thick Si-doped n-Al0.15Ga0.85N layer, five pairs of Al0.15Ga0.85N (12 nm)/GaN (3nm) MQWs, an Al0.2Ga0.8N electron blocking layer and a 120-nm-thick p-GaN contact layer. The nanopillar structure was fabricated by NSL technique, according to the schematic process flow illustrated in Fig. 1.
Fig. 1 Schematic process flow of fabricating AlGaN/GaN nanopillar LEDs using the nanosphere lithography and dry-etching.
First, a 200-nm SiO2 film was deposited on the AlGaN/GaN LED wafer by plasma enhanced chemical vapor deposition, and a highly ordered self-assembled monolayer of polystyrene (PS) nanospheres with a diameter of 630 nm was dip-coated on the wafer. Then, oxygen plasma was applied to the wafer using a reactive ion etching tool to shrink the nanospheres, that were the etching mask to define the SiO2 nanopillar in subsequent CF4-based inductively coupled plasma (ICP) etching. After the PS masks dissolving in toluene, the wafer was etched down to n-AlGaN layer using the SiO2 nanopillar mask by ICP etching with mixture plasmas of BCl3/Cl2/Ar. Finally, the SiO2 mask was removed by buffer oxide etchant and the nanopillar LEDs were treated in HCl to remove ICP-induced sidewall etching damages.

3. Results and discussions

Fig. 2 The top-view (a), tilted (b) and cross-sectional (c) SEM images of the AlGaN/GaN nanopillar structure.
Figures 2(a)-2(c) show typical top-view, tilted and cross-sectional SEM images of the AlGaN/GaN MQWs nanopillar structures, respectively. The nanopillars are in a highly uniform array determined by the highly ordered PS nanospheres. From Fig. 2(a), the nanopillar density is ~2.5 × 108 cm−2. As shown in Figs. 2(b) and 2(c), nanopillars consistently have smooth top and sidewall surfaces with narrow top and width bottom. The top diameter, bottom diameter and height average around 410 nm, 630 nm and 630 nm, respectively.

Fig. 3 The CL results of the AlGaN/GaN MQWs nanopillar LED sample measured at room temperature. The plane (a) and cross-sectional (b) monochromatic CL images of the nanopillar LEDs. The inset shows the CL spectrum of the nanopillar LEDs.
Figures 3(a) and 3(b) show the plan-view and cross-sectional monochromatic CL images of the nanopillar sample at an electron acceleration voltage of 5 kV. In Fig. 3(a), the emitting regions of the nanopillars are uniform, showing a strong peak around 354 nm and a weak emission one around 332 nm, corresponded with the MQWs and n-Al0.15Ga0.85N layer, respectively, as revealed in the spatial distribution monochromatic CL in Fig. 3 (b).

Fig. 4 PL spectra of as-grown sample and nanopillar sample at room temperature (a) and 10 K (b).
The PL spectra were measured using a 325-nm He-Cd laser and a spectrometer. Both the optical excitation and light collection were from samples’ top surfaces. Figures 4(a) and 4(b) show the room-temperature (RT, 300 K) and 10K PL spectra for both the as-grown and nanopillar samples, respectively, under identical condition. As shown in Fig. 4(a), the peak PL intensity of the nanopillar sample is increased by 2.3 times when compared with that of the as-grown sample at RT. Moreover, the small emission peak blue shift from 353.9 nm to 353.2 nm (7 meV) in the nanopillar sample can be attributed to the alleviated QCSE because of the strain relaxation in the MQWs region after fabrication of nanopillar structures [21

21. Q. Wang, J. Bai, Y. P. Gong, and T. Wang, “Influence of strain relaxation on the optical properties of InGaN/GaN multiple quantum well nanorods,” J. Phys. D Appl. Phys. 44(39), 395102 (2011). [CrossRef]

24

24. Y. Kawakami, A. Kaneta, L. Su, Y. Zhu, K. Okamoto, M. Funato, A. Kikuchi, and K. Kishino, “Optical properties of InGaN/GaN nanopillars fabricated by postgrowth chemically assisted ion beam etching,” J. Appl. Phys. 107(2), 023522 (2010). [CrossRef]

]. The reduced QCSE suggests the relieved band bending, the increased wave function overlap of electrons and holes and therefore the increase of IQE. In addition, the large difference of PL intensity at 10 K, shown in Fig. 4(b), indicates the enhanced LEE in the nanopillar sample, assuming that IQE equals to 100% for both samples at 10 K. Thus, the enhancement of room temperature PL intensity can be attributed to the increase of both IQE and LEE (mainly the light extraction enhancement from the top side) in the nanopillar sample.

Fig. 5 Arrhenius plots of the PL intensities of the as-grown and nanopillar samples as a function of temperature from 10 K to 300 K.
The ratio of the PL intensities of RT and 10 K is widely used to numerically evaluate the IQE at RT, assuming that the non-radiative recombination at 10 K is negligible and the corresponding IQE is 100%. Figure 5 shows the Arrhenius plots of the temperature-dependent PL intensities of these two samples from 10 K to 300 K. The RT IQEs are calculated to be 33% and 47% for the as-grown sample and the nanopillar sample, respectively, demonstrating a great increase of 42% for the nanopillar sample. In addition, in Fig. 5 the PL intensities of the as-grown and nanopillar samples sharply decreased when the temperatures were above 70 K and 160 K, respectively. The higher temperature for the nanopillar sample means that its non-radiative recombination centers need higher energy to be activated.

Time-resolved PL (TRPL) measurements were performed on the as-grown and nanopillar samples at 7 K using a 267-nm mode-locked Ti:sapphire laser (frequency: 76 MHz, pulse width: 150 fs). TRPL signals were collected by a stand streak-camera acquisition system with a resolution of 15 ps. As shown in Fig. 6, the TRPL spectra of these two samples both can be fitted with single exponential curves described by I(t)=I0exp(tτ), where I(t)is the PL intensity as a function of time (t), and τ is the photo-excited carrier lifetime. The best fitted τ for as-grown and nanopillar samples are 870 ps and 621 ps, respectively. It is commonly accepted that non-radiative recombination centers freeze up at low temperature [25

25. T. Onuma, S. F. Chichibu, A. Uedono, T. Sota, P. Cantu, T. M. Katona, J. F. Keading, S. Keller, U. K. Mishra, S. Nakamura, and S. P. DenBaars, “Radiative and nonradiative processes in strain-free AlxGa1-xN films studied by time-resolved photoluminescence and positron annihilation techniques,” J. Appl. Phys. 95(5), 2495 (2004). [CrossRef]

, 26

26. T. Koida, S. F. Chichibu, T. Sota, M. D. Craven, B. A. Haskell, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Improved quantum efficiency in nonpolar (112̄0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth,” Appl. Phys. Lett. 84(19), 3768 (2004). [CrossRef]

], so the shorter τ of the nanopillar sample indicates a faster radiative recombination rate, resulting from the improvement in the QCSE caused by the strain relaxation. This result is in accordance with the blue shift observed in RT PL spectra for the nanopillar sample.
Fig. 6 Time-resolved PL (TR-PL) spectra of the as-grown and nanopillar sample measured at low temperature (7 K).

Fig. 7 Raman spectra of the E2 (high) phonon mode of the as-grown and nanopillar samples, the inset shows a typical Raman spectra of the as-grown and nanopillar samples.
Micro-Raman measurement was carried out to confirm the strain state in as-grown and nanopillar samples. The Raman spectra are shown in Fig. 7. The spectra are mainly dominated by strong E2(high), E2(low), A1(LO) phonon modes. Usually, the E2(high) phonon mode is used to represent the stress state in the epitaxial layers, and the in-plane compressive stress σ of epitaxial layers can be expressed by the following equation [27

27. P. Puech, F. Demangeot, J. Frandon, C. Pinquier, M. Kuball, V. Domnich, and Y. Gogotsi, “GaN nanoindentation: A micro-Raman spectroscopy study of local strain fields,” J. Appl. Phys. 96(5), 2853–2856 (2004). [CrossRef]

]: ωE2(high)ω0=Cσ, where C is the biaxial strain coefficient (−2.25 cm−1/GPa for GaN), ωE2(high)and ω0 are the Raman shifts for ωE2(high) mode of the GaN epitaxial layers in our study and the stress-free GaN, respectively. The ω0 value is reported to be 568.0 cm−1 [28

28. P. Perlin, C. Jauberthie-Carillon, J. P. Itie, A. San Miguel, I. Grzegory, and A. Polian, “Raman scattering and x-ray-absorption spectroscopy in gallium nitride under high pressure,” Phys. Rev. B Condens. Matter 45(1), 83–89 (1992).

]. However, the values of ωE2(high) for the as-grown and nanopillar samples are located at 574.3 cm−1 and 570.0 cm−1, respectively. The in-plane compressive stress σ in GaN layers of the as-grown and nanopillar samples can be estimated to be −2.8 GPa and −0.9 GPa, respectively. Therefore, the less in-plane compressive stress for nanopillar sample demonstrates that the strain relaxation has occurred in the epitaxial layers of the nanopillar sample.

Fig. 8 Comparison of FDTD simulations of light propagation in (a) as-grown LED sample and (b) nanopillar LED sample.
FDTD simulation was performed to investigate the effect of nanopillar structure on the LEE with a simplified 2D simulation model because of the symmetry of the nanopillars. Figures 8 (a) and 8(b) present the 2D distribution of the simulated near-field intensity of light propagation in as-grown and nanopillar LEDs,

Table 1. the LEE of different directions by FDTD simulation.

table-icon
View This Table
As shown in Table 1, the top-, bottom- and side-LEE for the nanopillar LED respectively is 2.2, 1.8 and 0.73 times of those for the as-grown LED. Although the side-LEE is decreased, the total-LEE is increased from 22.5% to 33.7% thanks to the greatly enhanced LEE in the vertical direction. The reasons are as follows. First, each nanopillar has an effect of waveguide to vertically confine photons. Second, photons extracted from the nanopillars’ sidewall can also propagate vertically due to Bragg scattering of nanopillars. Third, the etched p-GaN layer decreases the absorbing of photons.

4. Conclusion

In conclusion, we have fabricated highly uniform AlGaN/GaN nanopillar LED arrays using nanosphere lithography technique. The AlGaN/GaN MQWs in nanopillars emit at a wavelength of 353.2 nm. The strain relaxation due to the formation of nanopillar MQWs results in three main effects compared with the as-grown sample. First, RT PL peak wavelength displays an approximate blue shift of 7 meV. Second, the IQE of nanopillar sample is improved by 42% suggested by temperature-dependent PL measurements. Third, the carrier lifetime at 7 K decreases, and the corresponding radiative recombination rate increases. Additionally, FDTD simulation has demonstrated that more photons are able to propagate vertically in the nanopillar MQW LED, thereby increasing the total LEE from 22.5% to 33.7%.

Acknowledgments

This work was supported by the National Natural Sciences Foundation of China under Grant No. 61376090 and 61376047 and 61204053 and 61006038 and 51102226, by the National High Technology Program of China under Grant No. 2014AA032608 and No. 2011AA03A111 and the Thousand Talent Program for Young Outstanding Scientists.

References and links

1.

M. Asif Khan, M. Shatalov, H. P. Maruska, H. M. Wang, and E. Kuokstis, “III–Nitride UV Devices,” Jpn. J. Appl. Phys. 44(10), 7191–7206 (2005). [CrossRef]

2.

Z. Lochner, T.-T. Kao, Y.-S. Liu, X.-H. Li, M. Mahbub Satter, S.-C. Shen, P. Douglas Yoder, J.-H. Ryou, R. D. Dupuis, Y. Wei, H. Xie, A. Fischer, and F. A. Ponce, “Deep-ultraviolet lasing at 243 nm from photo-pumped AlGaN/AlN heterostructure on AlN substrate,” Appl. Phys. Lett. 102(10), 101110 (2013). [CrossRef]

3.

D. Miller, D. Chemla, T. Damen, A. Gossard, W. Wiegmann, T. Wood, and C. Burrus, “Band-Edge Electroabsorption in Quantum Well Structures: The Quantum-Confined Stark Effect,” Phys. Rev. Lett. 53(22), 2173–2176 (1984). [CrossRef]

4.

J. S. Im, H. Kollmer, J. Off, A. Sohmer, F. Scholz, and A. Hangleiter, “Reduction of oscillator strength due to piezoelectric fields in GaN/AlxGa1-xN quantum wells,” Phys. Rev. B 57(16), R9435–R9438 (1998). [CrossRef]

5.

Y. Y. Zhang, H. Z. Xie, H. Y. Zheng, T. B. Wei, H. Yang, J. Li, X. Y. Yi, X. Y. Song, G. H. Wang, and J. M. Li, “Light extraction efficiency improvement by multiple laser stealth dicing in InGaN-based blue light-emitting diodes,” Opt. Express 20(6), 6808–6815 (2012). [CrossRef] [PubMed]

6.

A. Khan, K. Balakrishnan, and T. Katona, “Ultraviolet light-emitting diodes based on group three nitrides,” Nat. Photonics 2(2), 77–84 (2008). [CrossRef]

7.

T. Nishida, N. Kobayashi, and T. Ban, “GaN-free transparent ultraviolet light-emitting diodes,” Appl. Phys. Lett. 82(1), 1 (2003). [CrossRef]

8.

M. Shatalov, W. Sun, A. Lunev, X. Hu, A. Dobrinsky, Y. Bilenko, J. Yang, M. Shur, R. Gaska, C. Moe, G. Garrett, and M. Wraback, “AlGaN Deep-Ultraviolet Light-Emitting Diodes with External Quantum Efficiency above 10%,” Appl. Phys. Express 5(8), 082101 (2012). [CrossRef]

9.

P. Dong, J. Yan, J. Wang, Y. Zhang, C. Geng, T. Wei, P. Cong, Y. Zhang, J. Zeng, Y. Tian, L. Sun, Q. Yan, J. Li, S. Fan, and Z. Qin, “282-nm AlGaN-based deep ultraviolet light-emitting diodes with improved performance on nano-patterned sapphire substrates,” Appl. Phys. Lett. 102(24), 241113 (2013). [CrossRef]

10.

J. Bai, Q. Wang, and T. Wang, “Characterization of InGaN-based nanorod light emitting diodes with different indium compositions,” J. Appl. Phys. 111(11), 113103 (2012). [CrossRef]

11.

C. H. Liao, W. M. Chang, H. S. Chen, C. Y. Chen, Y. F. Yao, H. T. Chen, C. Y. Su, S. Y. Ting, Y. W. Kiang, and C. C. Yang, “Geometry and composition comparisons between c-plane disc-like and m-plane core-shell InGaN/GaN quantum wells in a nitride nanorod,” Opt. Express 20(14), 15859–15871 (2012). [CrossRef] [PubMed]

12.

V. Ramesh, A. Kikuchi, K. Kishino, M. Funato, and Y. Kawakami, “Strain relaxation effect by nanotexturing InGaN/GaN multiple quantum well,” J. Appl. Phys. 107(11), 114303 (2010). [CrossRef]

13.

Y. Y. Huang, L. Y. Chen, C. H. Chang, Y. H. Sun, Y. W. Cheng, M. Y. Ke, Y. H. Lu, H. C. Kuo, and J. Huang, “Investigation of low-temperature electroluminescence of InGaN/GaN based nanorod light emitting arrays,” Nanotechnology 22(4), 045202 (2011). [CrossRef] [PubMed]

14.

H. Sekiguchi, K. Kishino, and A. Kikuchi, “Emission color control from blue to red with nanocolumn diameter of InGaN/GaN nanocolumn arrays grown on same substrate,” Appl. Phys. Lett. 96(23), 231104 (2010). [CrossRef]

15.

S. Li and A. Waag, “GaN based nanorods for solid state lighting,” J. Appl. Phys. 111(7), 071101 (2012). [CrossRef]

16.

C.-H. Chang, L.-Y. Chen, L.-C. Huang, Y.-T. Wang, T.-C. Lu, and J. J. Huang, “Effects of Strains and Defects on the Internal Quantum Efficiency of InGaN/GaN Nanorod Light Emitting Diodes,” IEEE J. Quantum Electron. 48(4), 551–556 (2012). [CrossRef]

17.

K. H. Li and H. W. Choi, “Air-spaced GaN nanopillar photonic band gap structures patterned by nanosphere lithography,” J. Appl. Phys. 109(2), 023107 (2011). [CrossRef]

18.

L. Y. Chen, Y. Y. Huang, C. H. Chang, Y. H. Sun, Y. W. Cheng, M. Y. Ke, C. P. Chen, and J. J. Huang, “High performance InGaN/GaN nanorod light emitting diode arrays fabricated by nanosphere lithography and chemical mechanical polishing processes,” Opt. Express 18(8), 7664–7669 (2010). [CrossRef] [PubMed]

19.

C. L. Cheung, R. J. Nikolic, C. E. Reinhardt, and T. F. Wang, “Fabrication of nanopillars by nanosphere lithography,” Nanotechnology 17(5), 1339–1343 (2006). [CrossRef]

20.

S. D. Hersee, X. Y. Sun, and X. Wang, “The controlled growth of GaN nanowires,” Nano Lett. 6(8), 1808–1811 (2006). [CrossRef] [PubMed]

21.

Q. Wang, J. Bai, Y. P. Gong, and T. Wang, “Influence of strain relaxation on the optical properties of InGaN/GaN multiple quantum well nanorods,” J. Phys. D Appl. Phys. 44(39), 395102 (2011). [CrossRef]

22.

L. Dai, B. Zhang, J. Y. Lin, and H. X. Jiang, “Comparison of optical transitions in InGaN quantum well structures and microdisks,” J. Appl. Phys. 89(9), 4951 (2001). [CrossRef]

23.

S. Keller, C. Schaake, N. A. Fichtenbaum, C. J. Neufeld, Y. Wu, K. McGroddy, A. David, S. P. DenBaars, C. Weisbuch, J. S. Speck, and U. K. Mishra, “Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN/GaN multi-quantum wells,” J. Appl. Phys. 100(5), 054314 (2006). [CrossRef]

24.

Y. Kawakami, A. Kaneta, L. Su, Y. Zhu, K. Okamoto, M. Funato, A. Kikuchi, and K. Kishino, “Optical properties of InGaN/GaN nanopillars fabricated by postgrowth chemically assisted ion beam etching,” J. Appl. Phys. 107(2), 023522 (2010). [CrossRef]

25.

T. Onuma, S. F. Chichibu, A. Uedono, T. Sota, P. Cantu, T. M. Katona, J. F. Keading, S. Keller, U. K. Mishra, S. Nakamura, and S. P. DenBaars, “Radiative and nonradiative processes in strain-free AlxGa1-xN films studied by time-resolved photoluminescence and positron annihilation techniques,” J. Appl. Phys. 95(5), 2495 (2004). [CrossRef]

26.

T. Koida, S. F. Chichibu, T. Sota, M. D. Craven, B. A. Haskell, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Improved quantum efficiency in nonpolar (112̄0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth,” Appl. Phys. Lett. 84(19), 3768 (2004). [CrossRef]

27.

P. Puech, F. Demangeot, J. Frandon, C. Pinquier, M. Kuball, V. Domnich, and Y. Gogotsi, “GaN nanoindentation: A micro-Raman spectroscopy study of local strain fields,” J. Appl. Phys. 96(5), 2853–2856 (2004). [CrossRef]

28.

P. Perlin, C. Jauberthie-Carillon, J. P. Itie, A. San Miguel, I. Grzegory, and A. Polian, “Raman scattering and x-ray-absorption spectroscopy in gallium nitride under high pressure,” Phys. Rev. B Condens. Matter 45(1), 83–89 (1992).

OCIS Codes
(160.4760) Materials : Optical properties
(230.3670) Optical devices : Light-emitting diodes
(250.5230) Optoelectronics : Photoluminescence
(220.4241) Optical design and fabrication : Nanostructure fabrication

ToC Category:
Light-Emitting Diodes

History
Original Manuscript: November 29, 2013
Revised Manuscript: January 23, 2014
Manuscript Accepted: January 25, 2014
Published: February 10, 2014

Citation
Peng Dong, Jianchang Yan, Yun Zhang, Junxi Wang, Chong Geng, Haiyang Zheng, Xuecheng Wei, Qingfeng Yan, and Jinmin Li, "Optical properties of nanopillar AlGaN/GaN MQWs for ultraviolet light-emitting diodes," Opt. Express 22, A320-A327 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-S2-A320


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References

  1. M. Asif Khan, M. Shatalov, H. P. Maruska, H. M. Wang, and E. Kuokstis, “III–Nitride UV Devices,” Jpn. J. Appl. Phys.44(10), 7191–7206 (2005). [CrossRef]
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