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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 6 — Mar. 14, 2011
  • pp: 5442–5450
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Opposite carrier dynamics and optical absorption characteristics under external electric field in nonpolar vs. polar InGaN/GaN based quantum heterostructures

Emre Sari, Sedat Nizamoglu, Jung-Hun Choi, Seung-Jae Lee, Kwang-Hyeon Baik, In-Hwan Lee, Jong-Hyeob Baek, Sung-Min Hwang, and Hilmi Volkan Demir  »View Author Affiliations


Optics Express, Vol. 19, Issue 6, pp. 5442-5450 (2011)
http://dx.doi.org/10.1364/OE.19.005442


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Abstract

We report on the electric field dependent carrier dynamics and optical absorption in nonpolar a-plane GaN-based quantum heterostructures grown on r-plane sapphire, which are surprisingly observed to be opposite to those polar ones of the same materials system and similar structure grown on c-plane. Confirmed by their time-resolved photoluminescence measurements and numerical analyses, we show that carrier lifetimes increase with increasing external electric field in nonpolar InGaN/GaN heterostructure epitaxy, whereas exactly the opposite occurs for the polar epitaxy. Moreover, we observe blue-shifting absorption spectra with increasing external electric field as a result of reversed quantum confined Stark effect in these polar structures, while we observe red-shifting absorption spectra with increasing external electric field because of standard quantum confined Stark effect in the nonpolar structures. We explain these opposite behaviors of external electric field dependence with the changing overlap of electron and hole wavefunctions in the context of Fermi’s golden rule.

© 2011 OSA

1. Introduction

Such polarization-free (nonpolar) planes are m- and a-planes of the GaN’s wurtzite crystal [9

9. C. Wetzel, M. Zhu, J. Senawiratne, T. Detchprohm, P. D. Persans, L. Liu, E. A. Preble, and D. Hanser, “Light-emitting diode development on polar and non-polar GaN substrates,” J. Cryst. Growth 310(17), 3987–3991 (2008). [CrossRef]

]. To date, many techniques have previously been proposed for obtaining high-quality nonpolar GaN crystals [10

10. T. Paskova, R. Kroeger, D. Hommel, P. P. Paskov, B. Monemar, E. Preble, A. Hanser, N. M. Williams, and M. Tutor, “Nonpolar a- and m-plane bulk GaN sliced from boules: structural and optical characteristics,” Phys. Status Solidi 4(7), 1610–1642 (2007).

]. Also, LEDs [11

11. K. Okamoto, H. Ohta, D. Nakagawa, M. Sonobe, J. Ichihara, and H. Takasu, “Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals,” Jpn. J. Appl. Phys. 45(45), L1197–L1199 (2006). [CrossRef]

] and LDs [12

12. M. C. Schmidt, K.-C. Kim, R. M. Farrell, D. F. Feezell, D. A. Cohen, M. Saito, K. Fujito, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Demonstration of Nonpolar m-Plane InGaN/GaN Laser Diodes,” Jpn. J. Appl. Phys. 46(9), L190–L191 (2007). [CrossRef]

] have been demonstrated using these techniques. Very few of these prior works involved a feasible and efficient process, though. In a very recent work, Hwang et al. [13

13. S.-M. Hwang, Y.-G. Seo, K.-H. Baik, I.-S. Cho, J.-H. Baek, S.-K. Jung, T. G. Kim, and M.-W. Cho, “Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate,” Appl. Phys. Lett. 95(7), 071101 (2009). [CrossRef]

] made it possible to grow a-plane GaN on r-plane sapphire by reducing defect densities and demonstrated working light emitting diodes incorporating these nonpolar InGaN/GaN quantum structures, using metal-organic chemical vapor deposition (MOCVD) technique while avoiding the need for growing on a very thick (>10 μm) GaN template.

In this paper, different than prior works of our group and others, we present a study on the field dependent carrier dynamics and optical absorption characteristics of InGaN/GaN quantum heterostructures in nonpolar crystal orientation on a-plane to compare against those in polar orientation on c-plane. In both cases, the quantum structures are housed in the intrinsic region of a p-i-n diode, with the p-region on the top. Using these comparative sets of nonpolar vs. polar quantum heterostructures, we observe surprisingly a completely opposite behavior in the external electric field dependence of their carrier lifetimes and optical absorptions in their respective reverse and forward biases in both time-resolved photoluminescence (TRPL) and steady-state photocurrent measurements and numerical analyses. Our results for the polar, c-plane grown devices are in agreement with the previously reported results, in which decreased carrier lifetime [17

17. E. Sari, S. Nizamoglu, I.-H. Lee, J.-H. Baek, and H. V. Demir, “Electric field dependent radiative decay kinetics of polar InGaN/GaN quantum heterostructures at low fields,” Appl. Phys. Lett. 94(21), 211107 (2009). [CrossRef]

19

19. Y. D. Jho, Y. S. Yahng, E. Oh, and D. S. Kim, “Measurement of piezoelectric field and tunneling times in strongly biased InGaN/GaN quantum wells,” Appl. Phys. Lett. 79(8), 1130 (2001). [CrossRef]

] and blue-shifting absorption edge [5

5. E. Sari, S. Nizamoglu, T. Ozel, and H. V. Demir, “Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift,” Appl. Phys. Lett. 90(1), 011101 (2007). [CrossRef]

] were observed with increasing reverse bias voltages.

2. Growth and fabrication

The quantum heterostructures studied in this work were epitaxially grown on r-plane and c-plane sapphire substrates, both using MOCVD as described elsewhere previously (e.g., see [13

13. S.-M. Hwang, Y.-G. Seo, K.-H. Baik, I.-S. Cho, J.-H. Baek, S.-K. Jung, T. G. Kim, and M.-W. Cho, “Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate,” Appl. Phys. Lett. 95(7), 071101 (2009). [CrossRef]

] and [14

14. G. A. Garrett, H. Shen, M. Wraback, A. Tyagi, M. C. Schmidt, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Comparison of time-resolved photoluminescence from InGaN single quantum wells grown on nonpolar and semipolar bulk GaN substrates,” Phys. Status Solidi C 6(S2), S800–S803 (2009). [CrossRef]

], respectively). They were incorporated in a p-i-n diode architecture, and their n-type layer was on the bottom while their p-type layer was on the top. These epi-structures included (i) two 7 nm thick In0.20Ga0.80N quantum wells separated by a 12 nm GaN barrier in the nonpolar case and (ii) five 2.5 nm thick In0.18Ga0.82N quantum wells separated by 7.5 nm GaN barriers in the polar case. Although these multi-quantum well structures are slightly different, they are essentially the same type of uncoupled quantum structures, with their peak photoluminescence emission wavelengths close to each other, both exhibiting strong emission around λ~500 nm. Moreover, for both structures, the electron concentrations throughout the active (multiple quantum well) region were approximately 4x1017 cm−3. Subsequent to their epitaxial growth, the devices were fabricated in a clean room environment using the same standard lithography, reactive ion etching and metal evaporation/sputtering steps. The devices were then diced and wire-bonded to metal can packages for compact and reproducible device characterization.

3. Materials and device characterization

The photoluminescence (PL) spectra of our quantum structure samples were measured using a He-Cd laser to pump at an excitation wavelength of 325 nm and a spectrometer to collect the emission signal. From these PL spectra, using Gaussian fitting procedure, (i) a peak emission wavelength at 514 nm with a full width at half maximum (FWHM) of 43.1 nm for the nonpolar heterostructure on a-plane and (ii) a peak wavelength of 491 nm with a FWHM of 37.5 nm for the polar heterostructure on c-plane were obtained. Their measured photoluminescence spectra are shown in Fig. 1
Fig. 1 Normalized photoluminescence (PL) spectra of our InGaN/GaN based polar and nonpolar quantum heterostructures at room temperature. The dashed blue line shows the TRPL emission wavelength, 500 nm.
.

It is clear that for both epi-structures, the presented photoluminescence originates from the quantum well structures. Moreover, both exhibit electroluminescence when their devices are forward-biased as given in Fig. 2
Fig. 2 Normalized electroluminescence (EL) spectra of our devices based on polar and nonpolar InGaN/GaN quantum heterostructures, both measured at a constant driving current of 20 mA at room temperature.
.

3.1 Electric field dependence of carrier lifetimes

The carrier lifetimes (τ) of these quantum structures were measured at room temperature using a commercially available time-resolved photoluminescence setup (from PicoQuant GmbH) that contains an InGaN/AlGaN based pump diode laser, emitting at 375 nm and operated in pulsed mode. The experimental conditions were kept the same for both devices. Average and peak intensities of laser excitation were kept at low values, at around 3 and 6 W/cm2, respectively, to avoid band filling effect and thus evolution of higher energy states. Moreover, at such laser excitation intensity levels, with the given carrier densities in the active region, the effect of Auger recombination on the carrier lifetimes is insignificant [20

20. Y. C. Shen, G. O. Mueller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames, “Auger recombination in InGaN measured by photoluminescence,” Appl. Phys. Lett. 91(14), 141101 (2007). [CrossRef]

]. The measurement setup also consists of a monochromator, a photomultiplier tube and controller electronics. We set the pass band center wavelength of the monochromator to 500 nm for both sets of measurements. As depicted with a straight dashed (blue) line in the PL spectra of both epi-structures (Fig. 1), 500 nm corresponds to a strong emission wavelength.

Similarly, Fig. 4
Fig. 4 Room temperature time-resolved photoluminescence (RT-TRPL) traces and numerical fits of our device with nonpolar InGaN/GaN quantum heterostructures under different bias levels.
shows the photoluminescence decay time traces of nonpolar epitaxy on a-plane with respect to different levels of external electric field. For this set of epi-structure, the electric field dependence is observed to be in the opposite way, where the photoluminescence decays become slower as the external electric field is increased in reverse bias. This results from the reduced overlap integral of electron and hole wavefunctions in the initially nearly square potential well in response to an externally applied electric field. Nevertheless, with increasing reverse bias voltages, the overall time constant of nonradiative component does not decrease as much at low levels of the external electric fields. The nonpolar structure’s time-resolved photoluminescence profiles also exhibit faster decays, again opposite to the polar case, as the forward bias voltage is increased (where the lifetimes were measured down to the measurement limit of our optical experimental setup). Again, at such low voltage levels of forward bias, the decreased lifetimes can be explained through compensation of built-in voltage with the external electric field and at some field level, forming an almost perfectly square potential well, which would yield the shortest lifetime.

In our time-resolved analyses, we perform de-convolution of impulse response function (IRF) from the signal and apply a biexponential numerical fitting procedure with low error (χ2 close to unity) for all decay profiles. We then extract carrier lifetimes (τ) by averaging the time constants, τ1 and τ2, with their respective total intensities, i.e., their weights. Thus, the time constants we obtain in this procedure contain information on both slow and fast components of the overall decay profile. The corresponding numerical fits were provided in the decays. From these numerical analyses, we extract the carrier lifetimes as a function of external electric field for both structures as depicted in Fig. 5
Fig. 5 Carrier lifetime (τ) vs external electric field (E) for the polar and nonpolar devices. Note that here E is taken to be positive for the forward bias and negative for the reverse bias.
. These analysis results also reveal the opposite behavior in nonpolar vs. polar quantum heterostructures in terms of carrier lifetimes under electric field. Here, we present the lifetimes as a function of externally applied electric fields, rather than voltages, in order to make a meaningful comparison between the two sets of data. Hence, for both structures, we assume that the total voltage drop across the devices is in the depletion regions. We further assume that the depletion widths are 50 nm, and that they do not change by such low voltage application. With these approximations, we do not lose any generality for our points discussed in this paper. This opposite behavior could be qualitatively explained by quantum confined Stark effect (QCSE) and Fermi’s golden rule considering the increased vs. decreased squared-overlap integrals of electron and hole wavefunctions (under the assumption that the nonradiative components of the decays would not change with the external electric field within the range of interest) [14

14. G. A. Garrett, H. Shen, M. Wraback, A. Tyagi, M. C. Schmidt, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Comparison of time-resolved photoluminescence from InGaN single quantum wells grown on nonpolar and semipolar bulk GaN substrates,” Phys. Status Solidi C 6(S2), S800–S803 (2009). [CrossRef]

,16

16. E. Lioudakis, A. Othonos, E. Dimakis, E. Iliopoulos, and A. Georgakilas, “Ultrafast carrier dynamics in InxGa1−xN (0001) epilayers: Effects of high fluence excitation,” Appl. Phys. Lett. 88(12), 121128 (2006). [CrossRef]

].

3.2 Electric field dependence of optical absorption

We also comparatively investigated the external field dependent optical absorption in our polar and nonpolar InGaN/GaN based devices through photocurrent measurements. Our photocurrent setup consists of a Xenon lamp, monochromator, optical chopper, DC power supply and a lock-in amplifier. We measured the photocurrent both in our polar and nonpolar devices around the wavelength of their absorption edges at different reverse bias levels at room temperature. Here shown in a semilog plot of the photocurrent spectra in Fig. 6
Fig. 6 Photocurrent spectra of our device based on polar InGaN/GaN quantum heterostructures. The arrow indicates the blue shift of the absorption edge with the increasing reverse bias.
, the polar device exhibits a blue-shifting absorption edge with the applied field due to reversed quantum confined Stark effect.

In the opposite manner, for the nonpolar structure, we observe a red-shifting trend of the absorption edge, as a result of quantum confined Stark effect [21

21. D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter 32(2), 1043–1060 (1985). [CrossRef] [PubMed]

] that manifests itself as in other III-V systems such as InP/GaAs as in Fig. 7
Fig. 7 Photocurrent spectra of our device based on nonpolar InGaN/GaN quantum heterostructures. The arrow indicates the red shift of the absorption edge with the increasing reverse bias.
. Due to the narrower bandgap of the quantum well material, here for the nonpolar quantum structures the absorption edge is at longer wavelengths, around λ~500 nm.

4. Conclusion

In conclusion, we presented the opposite external electric field dependence of carrier lifetimes and optical absorption characteristics in c-plane grown polar vs. a-plane grown nonpolar InGaN/GaN quantum heterostructures. We showed using time-resolved photoluminescence measurements that carrier lifetimes decrease with increasing external electric fields in polar quantum epi-structures, whereas the opposite occurs in nonpolar quantum epi-structures. In addition, we presented the blue shift of the absorption edge in polar quantum heterostructures and the red shift of the absorption edge in nonpolar heterostructures. We explained these opposite behaviors in the context of Fermi’s golden rule as well as quantum confined Stark effect.

Acknowledgments

This work is supported by EU-FP7 Nanophotonics4Energy NoE, and TUBITAK Grant Nos. EEEAG 109E002, 109E004, and 110E010. H.V.D. acknowledges support from ESF-EURYI and TUBA GEBIP, and E.S. from TUBITAK-BIDEB 2211.

References and links

1.

S. Nakamura, M. Senoh, N. Iwasa, and S. Nagahama, “High power InGaN single-quantum-well-structure blue and violet light-emitting diodes,” Appl. Phys. Lett. 67(13), 1868–1870 (1995). [CrossRef]

2.

S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, and H. Kiyoku, “Room-temperature continuous-wave operation of InGaN multi-quantum-well structure laser diodes,” Appl. Phys. Lett. 69(26), 4056–4058 (1996). [CrossRef]

3.

S. Nizamoglu, G. Zengin, and H. V. Demir, “Color-converting combinations of nanocrystal emitters for warm-white light generation with high color rendering index,” Appl. Phys. Lett. 92(3), 031102–031104 (2008). [CrossRef]

4.

H. X. Jiang, S. X. Jin, J. Li, J. Shakya, and J. Y. Lin, “III-nitride blue microdisplays,” Appl. Phys. Lett. 78(9), 1303–1305 (2001). [CrossRef]

5.

E. Sari, S. Nizamoglu, T. Ozel, and H. V. Demir, “Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift,” Appl. Phys. Lett. 90(1), 011101 (2007). [CrossRef]

6.

D. Walker, E. Monroy, P. Kung, J. Wu, M. Hamilton, F. J. Sanchez, J. Diaz, and M. Razeghi, “High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN,” Appl. Phys. Lett. 74(5), 762 (1999). [CrossRef]

7.

J. Goldberger, R. He, Y. Zhang, S. Lee, H. Yan, H.-J. Choi, and P. Yang, “Single-crystal gallium nitride nanotubes,” Nature 422(6932), 599–602 (2003). [CrossRef] [PubMed]

8.

B. Monemar and G. Pozina, ““Group III-nitride based hetero and quantum structures,” Prog. Quantum Electron. 24(6), 239–290 (2000). [CrossRef]

9.

C. Wetzel, M. Zhu, J. Senawiratne, T. Detchprohm, P. D. Persans, L. Liu, E. A. Preble, and D. Hanser, “Light-emitting diode development on polar and non-polar GaN substrates,” J. Cryst. Growth 310(17), 3987–3991 (2008). [CrossRef]

10.

T. Paskova, R. Kroeger, D. Hommel, P. P. Paskov, B. Monemar, E. Preble, A. Hanser, N. M. Williams, and M. Tutor, “Nonpolar a- and m-plane bulk GaN sliced from boules: structural and optical characteristics,” Phys. Status Solidi 4(7), 1610–1642 (2007).

11.

K. Okamoto, H. Ohta, D. Nakagawa, M. Sonobe, J. Ichihara, and H. Takasu, “Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals,” Jpn. J. Appl. Phys. 45(45), L1197–L1199 (2006). [CrossRef]

12.

M. C. Schmidt, K.-C. Kim, R. M. Farrell, D. F. Feezell, D. A. Cohen, M. Saito, K. Fujito, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Demonstration of Nonpolar m-Plane InGaN/GaN Laser Diodes,” Jpn. J. Appl. Phys. 46(9), L190–L191 (2007). [CrossRef]

13.

S.-M. Hwang, Y.-G. Seo, K.-H. Baik, I.-S. Cho, J.-H. Baek, S.-K. Jung, T. G. Kim, and M.-W. Cho, “Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate,” Appl. Phys. Lett. 95(7), 071101 (2009). [CrossRef]

14.

G. A. Garrett, H. Shen, M. Wraback, A. Tyagi, M. C. Schmidt, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Comparison of time-resolved photoluminescence from InGaN single quantum wells grown on nonpolar and semipolar bulk GaN substrates,” Phys. Status Solidi C 6(S2), S800–S803 (2009). [CrossRef]

15.

M. Häberlen, T. J. Badcock, M. A. Moram, J. L. Hollander, M. J. Kappers, P. Dawson, C. J. Humphreys, and R. A. Oliver, “Low temperature photoluminescence and cathodoluminescence studies of nonpolar GaN grown using epitaxial lateral overgrowth,” J. Appl. Phys. 108(3), 033523–033529 (2010). [CrossRef]

16.

E. Lioudakis, A. Othonos, E. Dimakis, E. Iliopoulos, and A. Georgakilas, “Ultrafast carrier dynamics in InxGa1−xN (0001) epilayers: Effects of high fluence excitation,” Appl. Phys. Lett. 88(12), 121128 (2006). [CrossRef]

17.

E. Sari, S. Nizamoglu, I.-H. Lee, J.-H. Baek, and H. V. Demir, “Electric field dependent radiative decay kinetics of polar InGaN/GaN quantum heterostructures at low fields,” Appl. Phys. Lett. 94(21), 211107 (2009). [CrossRef]

18.

Y. D. Jho, J. S. Yahng, E. Oh, and D. S. Kim, “Field-dependent carrier decay dynamics in strained InxGa1-xN/GaN quantum wells,” Phys. Rev. B 66(3), 035334 (2002). [CrossRef]

19.

Y. D. Jho, Y. S. Yahng, E. Oh, and D. S. Kim, “Measurement of piezoelectric field and tunneling times in strongly biased InGaN/GaN quantum wells,” Appl. Phys. Lett. 79(8), 1130 (2001). [CrossRef]

20.

Y. C. Shen, G. O. Mueller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames, “Auger recombination in InGaN measured by photoluminescence,” Appl. Phys. Lett. 91(14), 141101 (2007). [CrossRef]

21.

D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter 32(2), 1043–1060 (1985). [CrossRef] [PubMed]

OCIS Codes
(160.4760) Materials : Optical properties
(160.6000) Materials : Semiconductor materials
(230.0250) Optical devices : Optoelectronics

ToC Category:
Instrumentation, Measurement, and Metrology

History
Original Manuscript: December 22, 2010
Revised Manuscript: February 23, 2011
Manuscript Accepted: February 25, 2011
Published: March 8, 2011

Citation
Emre Sari, Sedat Nizamoglu, Jung-Hun Choi, Seung-Jae Lee, Kwang-Hyeon Baik, In-Hwan Lee, Jong-Hyeob Baek, Sung-Min Hwang, and Hilmi Volkan Demir, "Opposite carrier dynamics and optical absorption characteristics under external electric field in nonpolar vs. polar InGaN/GaN based quantum heterostructures," Opt. Express 19, 5442-5450 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-6-5442


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References

  1. S. Nakamura, M. Senoh, N. Iwasa, and S. Nagahama, “High power InGaN single-quantum-well-structure blue and violet light-emitting diodes,” Appl. Phys. Lett. 67(13), 1868–1870 (1995). [CrossRef]
  2. S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, and H. Kiyoku, “Room-temperature continuous-wave operation of InGaN multi-quantum-well structure laser diodes,” Appl. Phys. Lett. 69(26), 4056–4058 (1996). [CrossRef]
  3. S. Nizamoglu, G. Zengin, and H. V. Demir, “Color-converting combinations of nanocrystal emitters for warm-white light generation with high color rendering index,” Appl. Phys. Lett. 92(3), 031102–031104 (2008). [CrossRef]
  4. H. X. Jiang, S. X. Jin, J. Li, J. Shakya, and J. Y. Lin, “III-nitride blue microdisplays,” Appl. Phys. Lett. 78(9), 1303–1305 (2001). [CrossRef]
  5. E. Sari, S. Nizamoglu, T. Ozel, and H. V. Demir, “Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift,” Appl. Phys. Lett. 90(1), 011101 (2007). [CrossRef]
  6. D. Walker, E. Monroy, P. Kung, J. Wu, M. Hamilton, F. J. Sanchez, J. Diaz, and M. Razeghi, “High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN,” Appl. Phys. Lett. 74(5), 762 (1999). [CrossRef]
  7. J. Goldberger, R. He, Y. Zhang, S. Lee, H. Yan, H.-J. Choi, and P. Yang, “Single-crystal gallium nitride nanotubes,” Nature 422(6932), 599–602 (2003). [CrossRef] [PubMed]
  8. B. Monemar and G. Pozina, ““Group III-nitride based hetero and quantum structures,” Prog. Quantum Electron. 24(6), 239–290 (2000). [CrossRef]
  9. C. Wetzel, M. Zhu, J. Senawiratne, T. Detchprohm, P. D. Persans, L. Liu, E. A. Preble, and D. Hanser, “Light-emitting diode development on polar and non-polar GaN substrates,” J. Cryst. Growth 310(17), 3987–3991 (2008). [CrossRef]
  10. T. Paskova, R. Kroeger, D. Hommel, P. P. Paskov, B. Monemar, E. Preble, A. Hanser, N. M. Williams, and M. Tutor, “Nonpolar a- and m-plane bulk GaN sliced from boules: structural and optical characteristics,” Phys. Status Solidi 4(7), 1610–1642 (2007).
  11. K. Okamoto, H. Ohta, D. Nakagawa, M. Sonobe, J. Ichihara, and H. Takasu, “Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals,” Jpn. J. Appl. Phys. 45(45), L1197–L1199 (2006). [CrossRef]
  12. M. C. Schmidt, K.-C. Kim, R. M. Farrell, D. F. Feezell, D. A. Cohen, M. Saito, K. Fujito, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Demonstration of Nonpolar m-Plane InGaN/GaN Laser Diodes,” Jpn. J. Appl. Phys. 46(9), L190–L191 (2007). [CrossRef]
  13. S.-M. Hwang, Y.-G. Seo, K.-H. Baik, I.-S. Cho, J.-H. Baek, S.-K. Jung, T. G. Kim, and M.-W. Cho, “Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate,” Appl. Phys. Lett. 95(7), 071101 (2009). [CrossRef]
  14. G. A. Garrett, H. Shen, M. Wraback, A. Tyagi, M. C. Schmidt, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Comparison of time-resolved photoluminescence from InGaN single quantum wells grown on nonpolar and semipolar bulk GaN substrates,” Phys. Status Solidi C 6(S2), S800–S803 (2009). [CrossRef]
  15. M. Häberlen, T. J. Badcock, M. A. Moram, J. L. Hollander, M. J. Kappers, P. Dawson, C. J. Humphreys, and R. A. Oliver, “Low temperature photoluminescence and cathodoluminescence studies of nonpolar GaN grown using epitaxial lateral overgrowth,” J. Appl. Phys. 108(3), 033523–033529 (2010). [CrossRef]
  16. E. Lioudakis, A. Othonos, E. Dimakis, E. Iliopoulos, and A. Georgakilas, “Ultrafast carrier dynamics in InxGa1−xN (0001) epilayers: Effects of high fluence excitation,” Appl. Phys. Lett. 88(12), 121128 (2006). [CrossRef]
  17. E. Sari, S. Nizamoglu, I.-H. Lee, J.-H. Baek, and H. V. Demir, “Electric field dependent radiative decay kinetics of polar InGaN/GaN quantum heterostructures at low fields,” Appl. Phys. Lett. 94(21), 211107 (2009). [CrossRef]
  18. Y. D. Jho, J. S. Yahng, E. Oh, and D. S. Kim, “Field-dependent carrier decay dynamics in strained InxGa1-xN/GaN quantum wells,” Phys. Rev. B 66(3), 035334 (2002). [CrossRef]
  19. Y. D. Jho, Y. S. Yahng, E. Oh, and D. S. Kim, “Measurement of piezoelectric field and tunneling times in strongly biased InGaN/GaN quantum wells,” Appl. Phys. Lett. 79(8), 1130 (2001). [CrossRef]
  20. Y. C. Shen, G. O. Mueller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames, “Auger recombination in InGaN measured by photoluminescence,” Appl. Phys. Lett. 91(14), 141101 (2007). [CrossRef]
  21. D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B Condens. Matter 32(2), 1043–1060 (1985). [CrossRef] [PubMed]

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