OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 22 — Nov. 4, 2013
  • pp: 26774–26779
« Show journal navigation

Near ultraviolet InGaN/AlGaN-based light-emitting diodes with highly reflective tin-doped indium oxide/Al-based reflectors

Chang-Hoon Choi, Jaecheon Han, Jae-Seong Park, and Tae-Yeon Seong  »View Author Affiliations


Optics Express, Vol. 21, Issue 22, pp. 26774-26779 (2013)
http://dx.doi.org/10.1364/OE.21.026774


View Full Text Article

Acrobat PDF (1466 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

The enhanced light output power of a InGaN/AlGaN-based light-emitting diodes (LEDs) using three different types of highly reflective Sn-doped indium oxide (ITO)/Al-based p-type reflectors, namely, ITO/Al, Cu-doped indium oxide (CIO)/s-ITO(sputtered)/Al, and Ag nano-dots(n-Ag)/CIO/s-ITO/Al, is presented. The ITO/Al-based reflectors exhibit lower reflectance (76 - 84% at 365 nm) than Al only reflector (91.1%). However, unlike Al only n-type contact, the ITO/Al-based contacts to p-GaN show good ohmic characteristics. Near-UV (365 nm) InGaN/AlGaN-based LEDs with ITO/Al, CIO/s-ITO/Al, and n-Ag/CIO/s-ITO/Al reflectors exhibit forward-bias voltages of 3.55, 3.48, and 3.34 V at 20 mA, respectively. The LEDs with the ITO/Al and CIO/s-ITO/Al reflectors exhibit 9.5% and 13.5% higher light output power (at 20 mA), respectively, than the LEDs with the n-Ag/CIO/s-ITO/Al reflector. The improved performance of near UV LEDs is attributed to the high reflectance and low contact resistivity of the ITO/Al-based reflectors, which are better than those of conventional Al-based reflectors.

© 2013 Optical Society of America

1. Introduction

AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) are of technological importance because of their potential applications in water purification and solid-state lighting [1

1. W. Sun, V. Adivarahan, M. Shatalov, Y. Lee, S. Wu, J. Yang, J. Zhang, and M. A. Khan, “Continuous wave milliwatt power AlGaN light emitting diodes at 280 nm,” Jpn. J. Appl. Phys. 43(No. 11A), L1419–L1421 (2004). [CrossRef]

3

3. H. Tsuzuki, F. Mori, K. Takeda, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “Novel UV devices on high-quality AlGaN using grooved underlying layer,” J. Cryst. Growth 311(10), 2860–2863 (2009). [CrossRef]

]. However, UV LEDs usually show very low external quantum efficiency (EQE) and high forward voltage due to poor light extraction efficiency and high contact resistance. Thus, to enhance the EQE, light extraction should be increased significantly. For GaN-based flip-chip LEDs and vertical geometry LEDs, metal-based reflectors, such as Ag- and Al-based schemes, have been widely used so as to increase the light extraction [4

4. J.-O. Song, D.-S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T.-Y. Seong, “Low-resistance and highly-reflective Zn-Ni solid solution/Ag ohmic contacts for flip-chip light-emitting diodes,” Appl. Phys. Lett. 83(24), 4990–4992 (2003). [CrossRef]

12

12. K. Takehara, K. Takeda, S. Ito, H. Aoshima, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, and H. Amano, “Indium-tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys. 51, 042101 (2012). [CrossRef]

]. Unlike Al reflector, however, the reflectance of Ag contact drops rapidly in the UV region. On the other hand, Al has a small work function and so serves as an electrode for n-type GaN [13

13. B. P. Luther, J. M. DeLucca, S. E. Mohney, and R. F. Karlicek Jr., “Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN,” Appl. Phys. Lett. 71(26), 3859–3861 (1997). [CrossRef]

]. Thus, to form Al-based ohmic contacts to p-GaN, a diffusion barrier was employed to hamper the indiffusion of Al into p-GaN. For instance, Song et al. [9

9. J.-O. Song, W.-G. Hong, J. S. Kwak, Y. Park, and T.-Y. Seong, “Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes,” Appl. Phys. Lett. 86(13), 133503 (2005). [CrossRef]

] used an Ag/tin-doped indium oxide (ITO) barrier layer to form high-quality p-type Al-based ohmic reflectors for flip-chip LEDs. The Ag/ITO/Al contacts exhibited a specific contact resistance of 8.7 × 10−5 Ωcm2 and a reflectance of 85% at 460 nm, which are much better than those of oxidized Ni/Au schemes. LEDs fabricated with the annealed Ag/ITO/Al reflector gave forward-bias voltages of 3.29–3.37 V at 20 mA. Furthermore, Lee et al. [11

11. W. H. Lee, D. J. Chae, D. Y. Kim, and T. G. Kim, “Improved electrical and optical properties of vertical GaN LEDs using fluorine-doped ITO/Al ohmic reflectors,” IEEE J. Quantum Electron. 47(10), 1277–1282 (2011). [CrossRef]

], investigating the effect of ITO surface conditions on the performance of ITO/Al ohmic reflectors, reported that the schemes produced a reflectance of 85% at 460 nm and a specific contact resistance of 2.03 × 10−3 Ω·cm2 after CF4 plasma-treatment. They attributed the improved electrical properties to the increase in the work function of ITO films through the formation of Al-F bonding. LEDs fabricated with the surface-treated reflectors showed 72% higher light output power at 60 mA than LEDs with untreated ITO/Al contacts. Recently, Takehara et al. [12

12. K. Takehara, K. Takeda, S. Ito, H. Aoshima, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, and H. Amano, “Indium-tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys. 51, 042101 (2012). [CrossRef]

], investigating a high-reflectivity electrode for 350 nm UV LEDs, reported that Al contact combined with an sputtered ITO interlayer exhibited high reflectance in the UV region and good contact characteristics. The UV LEDs fabricated with the ITO/Al reflector showed an operating voltage (5.2 V at 100 mA) similar to that (4.7 V) of a conventional Ni/Au contact and a high light output power comparable to that with Al only contacts. These results indicate that the development of optimized electrodes with low contact resistance and high reflectance in the UV region is crucial to the fabrication of high-external quantum efficiency UV LEDs. In this study, to reduce the forward bias voltage and to increase the output power of near UV InGaN/AlGaN-based LEDs, we investigated the addition effects of a Cu-doped indium oxide (CIO) layer, Ag nano-dots, and an ITO layer on the electrical and optical properties of Al only reflector. Near UV (365 nm) LEDs were fabricated with three different types of ITO/Al-based reflectors and their performance was compared.

2. Experimental

A metalorganic chemical vapor deposition system was used to grow near UV (365 nm) InGaN/AlGaN multiple quantum-well (MQW) LED structures on (0001) sapphire substrates. The LED structures consisted of a 2-nm-thick p-GaN:Mg layer, a 0.1-μm-thick p-AlGaN:Mg (na = 5 × 1017 cm−3) layer, a 20-nm-thick AlGaN electron blocking layer, a 100-nm-thick active layer, and a 200-nm-thick spreading layer, a 2.0-μm-thick n-AlGaN:Si (nd = 5 × 1018 cm−3) layer, and a 2.0-μm-thick undoped GaN layer on a sapphire substrate. Prior to metal deposition, all of the samples were treated with a diluted HCl (HCl: DI water = 1: 1) solution for 1 min, rinsed in DI water, and blown dry in a N2 stream. For LEDs fabricated with three different ITO-based ohmic contacts, mesa-shaped structures were defined by the standard photolithography and etched by inductively coupled plasma (ICP) etcher (OERIKON). For the first set, a 5-nm-thick Cu-doped indium oxide (CIO) layer was first e-beam evaporated on p-GaN using an In2O3 target containing 10 at% Cu, followed by the sputtering of a 10-nm-thick ITO layer, which was annealed at 500°C for 1 min in air to form ohmic contact. Then, a 200-nm-thick Al layer was deposited by e-beam. The sample was referred to herein as a “CIO/s-ITO/Al reflector”. For the second, a 1-nm-thick Ag layer was first e-beam evaporated, followed by annealing at 500°C for 1 min in air to form Ag nano-dots. Then, CIO (5nm) and ITO (10 nm) layers were consecutively deposited by e-beam and sputtering, respectively, after which the sample was annealed at 500°C. Then, a 200-nm-thick Al reflector was deposited by e-beam. The sample was referred to herein as a “n-Ag/CIO/s-ITO/Al reflector”. For the third, a ITO (10 nm) layer was first deposited by e-beam, (followed by annealing at 500°C), after which a 200-nm-thick Al layer was deposited. The sample was referred to herein as an “ITO/Al reflector”. For n-type ohmic contacts, Cr/Ni/Au (25/25/50 nm) layers were used. The schematic diagrams of LEDs are shown in Fig. 1
Fig. 1 Schematic diagram of LED structures fabricated with (a) CIO/ITO/Al and (b) Ag nano-dot/CIO/ITO/Al reflectors.
. Circular transfer length method (CTLM) patterns were defined by the standard photolithographic technique for measuring specific contact resistance. The outer radius of the CTLM patterns was fixed at 200 μm and the gap spacing between the outer and inner radii was varied from 5 to 40 μm. Current-voltage (I–V) measurements were carried out by a high-current source-measuring unit (Keithley 238). X-ray photoelectron spectroscopy (XPS, Sigma Probe model) was performed using an Al Kα X-ray source (1486.6 eV) in an UHV system in order to characterize the surface characteristics and to understand the improvement in the electrical properties. The optical outputs of UV-LED chips (500 × 250 μm2) were examined by means of a Newport dual channel powermeter.

3. Results and discussion

Figure 2
Fig. 2 The reflectance of Al contacts with different ITO-based multilayers. All of the layers were e-beam evaporated except for s-ITO that was sputter-deposited. The inset shows an AFM image of Ag nano-dots formed on p-GaN.
exhibits the reflectance of Al contacts with different ITO-based multilayers. The Al only reflector exhibits the highest reflectance across the whole wavelength region of 300 to 500 nm. The reflectance becomes significantly reduced when additional layers are introduced. For example, the Al only, n-Ag/CIO/s-ITO/Al, CIO/s-ITO/Al, s-ITO/Al, and ITO/Al samples show a reflectance of 91.1, 76, 80.5, 84.3, and 77.5% at 365 nm, respectively. The Ag/CIO/s-ITO/Al reflector shows the lowest reflectance due to the Ag nano-dots (the inset in Fig. 2). The atomic force microscopy (AFM) result shows that the nano-dots is varied from 5 to 20 nm in size. All of the layers were e-beam-evaporated except for s-ITO that was sputter-deposited. Although the s-ITO/Al sample exhibits higher reflectance than the e-beam-evaporated ITO/Al sample, it is non-ohmic due to plasma damage during sputtering (as shown in the inset of Fig. 3
Fig. 3 The typical I-V characteristics of near-UV (365 nm) InGaN/AlGaN MQW LEDs fabricated with Al contacts with different ITO-based multilayers. The inset shows the current-voltage characteristics of different ITO-based contacts.
). Thus, e-beam-evaporated ITO (referred to herein as “ITO”) was used in this study. It is noted that the reflectances (at 365 nm) of our ITO/Al-based contacts are higherthan those of the previously reported Al-based contacts [9

9. J.-O. Song, W.-G. Hong, J. S. Kwak, Y. Park, and T.-Y. Seong, “Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes,” Appl. Phys. Lett. 86(13), 133503 (2005). [CrossRef]

,11

11. W. H. Lee, D. J. Chae, D. Y. Kim, and T. G. Kim, “Improved electrical and optical properties of vertical GaN LEDs using fluorine-doped ITO/Al ohmic reflectors,” IEEE J. Quantum Electron. 47(10), 1277–1282 (2011). [CrossRef]

,14

14. D. L. Hibbard, S. P. Jung, C. Wang, D. Ullery, Y. S. Zhao, H. P. Lee, W. So, and H. Liu, “Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag,” Appl. Phys. Lett. 83(2), 311–313 (2003). [CrossRef]

], but comparable with the sputtered ITO (10 nm)/Al contacts [12

12. K. Takehara, K. Takeda, S. Ito, H. Aoshima, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, and H. Amano, “Indium-tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys. 51, 042101 (2012). [CrossRef]

].

Figure 3 exhibits the typical I-V characteristics of near-UV (365 nm) InGaN/AlGaN MQW LEDs fabricated with Al reflectors with different ITO-based layers. The LEDs with the n-Ag/CIO/s-ITO/Al reflector shows a forward-bias voltage of 3.34 V at an injection current of 20 mA, which is lower than those (3.48 and 3.55 V) of the LEDs with the CIO/s-ITO/Al and ITO/Al reflector, respectively. The series resistances of the LEDs with the n-Ag/CIO/s-ITO/Al, CIO/s-ITO/Al and ITO/Al reflectors were 11.8, 16.9, and 17.4 Ω, respectively. Note that the forward voltages are proportional to the specific contact resistances (the inset of Fig. 3). The specific contact resistances of the Ag/CIO/s-ITO/Al, CIO/s-ITO/Al, s-ITO/Al, and ITO/Al samples sample were measured to be 8.7 × 10−3, 6.3 × 10−2, 17.4, and 7.0 × 10−2 Ωcm2, respectively. In particular the n-Ag/CIO/s-ITO/Al contact showed better electrical properties than Ni/Au-based Al reflectors [14

14. D. L. Hibbard, S. P. Jung, C. Wang, D. Ullery, Y. S. Zhao, H. P. Lee, W. So, and H. Liu, “Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag,” Appl. Phys. Lett. 83(2), 311–313 (2003). [CrossRef]

].

Figure 4
Fig. 4 The light output-current (L-I) characteristics of near-UV LEDs fabricated with Al reflectors with different ITO-based multilayers.
shows the light output-current (L-I) characteristics of near UV LEDs fabricated with Al reflectors with different ITO-based ohmic contacts. The measurements show that the LEDs fabricated with the CIO/s-ITO/Al and ITO/Al reflectors yield 13.5 and 9.5% higher light output power (at 20 mA), respectively, than the LEDs with the n-Ag/CIO/s-ITO/Al reflector. A comparison shows that the output power is higher in the LEDs with the CIO/s-ITO/Al and ITO/Al reflectors, but the forward bias-voltage is lower in the LEDs with the Ag nano-dots combined reflector.

Figure 5
Fig. 5 The XPS Ga 2p core level spectra obtained from (a) CIO/s-ITO/Al and (b) n-Ag/CIO/s-ITO/Al contacts, both of which were annealed at 500°C before the deposition of an Al layer.
displays the XPS Ga 2p core level spectra obtained from CIO/s-ITO/Al and n-Ag/CIO/s-ITO/Al contacts after annealing at 500°C. XPS core-level peak fittings were carried out with a Shirley-type background and Lorentzian–Doniac–Sunsic curves convoluted with a Gaussian profile. The Ga 2p core levels for both the samples consist of Ga-N and Ga-O bonds. It is worth noting that after annealing, the Ga 2p core level for the n-Ag/CIO/s-ITO/Al contact shifted to the lower binding-energy side by 0.13 eV compared to that of the CIO/s-ITO/Al contact. This denotes that the surface Fermi level shifts toward the valence band edge [15

15. J.-O. Song and T.-Y. Seong, “Highly transparent Ag/SnO2 ohmic contact to p-type GaN for ultraviolet light-emitting diodes,” Appl. Phys. Lett. 85(26), 6374–6376 (2004). [CrossRef]

,16

16. J. H. Son, G. H. Jung, and J.-L. Lee, “Highly reflective Ag-Cu alloy-based ohmic contact on p-type GaN using Ru overlayer,” Opt. Lett. 33(24), 2907–2909 (2008). [CrossRef] [PubMed]

], resulting in a reduction in the band-bending of p-GaN, namely, a lowering of the Schottky barrier height (SBH). The Ga 2p peak shift indicates a change of the band-bending since theN 1s core level spectra exhibit a similar shift behavior [17

17. T. B. Massalski and H. Okamoto, Binary Alloy Phase Diagram (ASM International, metal parks, Ohio) (1990).

]. The normalized N/Ga atomic ratio for both the samples was obtained from the ratio of the integral intensity of the XPS N 1s peak to that of the Ga 2p peak (Ga-N bond) with reference to that of the as-deposited sample. The normalized N/Ga ratio was 1.08 ± 0.03. This shows that the p-GaN surface of the n-Ag/CIO/s-ITO/Al sample becomes Ga-deficient, compared with that of the CIO/s-ITO/Al contact, namely, the generation of Ga vacancies at the surface region.

The n-Ag/CIO/s-ITO/Al and CIO/s-ITO/Al reflectors exhibited better electrical properties than the ITO/Al reflectors after annealing (Fig. 3). The improvement could be understood by the formation of inhomogeneous Schottky barriers at the contact scheme/GaN interface due to the breaking-up of the CIO layer [18

18. J.-O. Song, S. Kwak, Y. Park, and T.-Y. Seong, “Improvement of the light output of InGaN-based light-emitting diodes using Cu-doped indium oxide/indium tin oxide p-type electrodes,” Appl. Phys. Lett. 86(21), 213505 (2005). [CrossRef]

]. It is assumed that there are only two uniform contacts at metal-semiconductor (MS) interface with inhomogeneous Schottky barriers [19

19. R. T. Tung, “Electron transport at metal-semiconductor interfaces: General theory,” Phys. Rev. B Condens. Matter 45(23), 13509–13523 (1992). [CrossRef] [PubMed]

] implies that the presence of the CIO nano-dots and the difference of the SBHs between CIO/GaN and ITO/GaN could increase the electric field at the MS interface. It was reported that the increase in the electric field causes a lowering of SBHs, leading to reduction in the specific contact resistance [20

20. S. K. Lee, C. M. Zettering, M. Ostling, I. Aberg, M. H. Magnusson, K. Deppert, L. E. Wernersson, L. Samuelson, and A. Litwin, “Reduction of the Schottky barrier height on silicon carbide using Au nano-particles,” Solid-State Electron. 46(9), 1433–1440 (2002). [CrossRef]

22

22. J. I. Sohn, J.-O. Song, D.-S. Leem, S. Lee, and T.-Y. Seong, “Formation of nonalloyed low resistance Ni/Au ohmic contacts to p-type GaN using Au nano-dots,” Electrochem. Solid-State Lett. 7(9), G179–G181 (2004). [CrossRef]

]. Assuming the same sheet resistance of p-GaN for the two samples, the lower forward voltage can be attributed to the lower SBH, namely, the lower contact resistivity. Furthermore, the best electrical behavior of the n-Ag/CIO/s-ITO/Al reflector could be explained by an additional effect, namely, reduction in the SBH caused by the shift of the surface Fermi level to the valence-band edge due to the increase in the acceptor-like Ga vacancies, as shown by the XPS results (Fig. 5) [6

6. J.-O. Song, J.-S. Ha, and T.-Y. Seong, “Ohmic-contact technology for GaN-based light-emitting diodes: role of P-type contact,” IEEE Trans. Electron. Dev. 57(1), 42–59 (2010). [CrossRef]

].

4. Summary and conclusion

We demonstrated the enhanced performance of near UV (365 nm) InGaN/AlGaN-based LEDs using highly reflective ITO/Al-based p-type reflectors. Unlike an Al only n-type contact, the ITO/Al-based multilayer contacts to p-GaN exhibited good ohmic behavior. Among the ITO/Al-based reflectors, the Ag nano-dot combined contacts showed the lowest contact resistivity, but the lowest reflectance (76%) at 365 nm. Near-UV LEDs with the ITO/Al and CIO/s-ITO/Al reflectors yielded a higher light output power (at 20 mA) than the LEDs with the n-Ag/CIO/s-ITO/Al reflector. Considering the fact that high-reflectance p-type ohmic contacts in the UV region are difficult to achieve, the ITO/Al-based multilayer reflectors with high reflectance or low forward bias voltages have the ability to serve as an important reflector for the fabrication of high-performance UV LEDs.

Acknowledgments

This work was supported by the industrial technology development program funded by the Ministry of Knowledge Economy (MKE), Korea and the industrial strategic technology development program, 10041878, Development of WPE 75% LED device process and standard evaluation technology funded by the MKE, Korea.

References and links

1.

W. Sun, V. Adivarahan, M. Shatalov, Y. Lee, S. Wu, J. Yang, J. Zhang, and M. A. Khan, “Continuous wave milliwatt power AlGaN light emitting diodes at 280 nm,” Jpn. J. Appl. Phys. 43(No. 11A), L1419–L1421 (2004). [CrossRef]

2.

M. Kneissl, Z. Yang, M. Teepe, C. Knollenberg, N. M. Johnson, A. Usikov, and V. Dmitriev, “Ultraviolet InAlGaN light emitting diodes grown on hydride vapor phase epitaxy AlGaN/sapphire templates,” Jpn. J. Appl. Phys. 45(5A), 3905–3908 (2006). [CrossRef]

3.

H. Tsuzuki, F. Mori, K. Takeda, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “Novel UV devices on high-quality AlGaN using grooved underlying layer,” J. Cryst. Growth 311(10), 2860–2863 (2009). [CrossRef]

4.

J.-O. Song, D.-S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T.-Y. Seong, “Low-resistance and highly-reflective Zn-Ni solid solution/Ag ohmic contacts for flip-chip light-emitting diodes,” Appl. Phys. Lett. 83(24), 4990–4992 (2003). [CrossRef]

5.

H. Kim, K. H. Baik, J. Cho, J. W. Lee, S. Yoon, H. Kim, S. N. Lee, C. Sone, Y. Park, and T.-Y. Seong, “High-reflectance and thermally stable AgCu alloy p-type reflectors for GaN-based light-emitting diodes,” IEEE Photon. Technol. Lett. 19(5), 336–338 (2007). [CrossRef]

6.

J.-O. Song, J.-S. Ha, and T.-Y. Seong, “Ohmic-contact technology for GaN-based light-emitting diodes: role of P-type contact,” IEEE Trans. Electron. Dev. 57(1), 42–59 (2010). [CrossRef]

7.

H. W. Jang and J.-L. Lee, “Mechanism for ohmic contact formation of Ni/Ag contacts on p-type GaN,” Appl. Phys. Lett. 85(24), 5920–5922 (2004). [CrossRef]

8.

I.-C. Chen, Y.-D. Chen, C.-C. Hsieh, C.-H. Kuo, and L.-C. Chang, “Highly reflective Ag/La bilayer ohmic contacts to p-type GaN,” J. Electrochem. Soc. 158(3), H285–H288 (2011). [CrossRef]

9.

J.-O. Song, W.-G. Hong, J. S. Kwak, Y. Park, and T.-Y. Seong, “Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes,” Appl. Phys. Lett. 86(13), 133503 (2005). [CrossRef]

10.

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010). [CrossRef]

11.

W. H. Lee, D. J. Chae, D. Y. Kim, and T. G. Kim, “Improved electrical and optical properties of vertical GaN LEDs using fluorine-doped ITO/Al ohmic reflectors,” IEEE J. Quantum Electron. 47(10), 1277–1282 (2011). [CrossRef]

12.

K. Takehara, K. Takeda, S. Ito, H. Aoshima, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, and H. Amano, “Indium-tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys. 51, 042101 (2012). [CrossRef]

13.

B. P. Luther, J. M. DeLucca, S. E. Mohney, and R. F. Karlicek Jr., “Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN,” Appl. Phys. Lett. 71(26), 3859–3861 (1997). [CrossRef]

14.

D. L. Hibbard, S. P. Jung, C. Wang, D. Ullery, Y. S. Zhao, H. P. Lee, W. So, and H. Liu, “Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag,” Appl. Phys. Lett. 83(2), 311–313 (2003). [CrossRef]

15.

J.-O. Song and T.-Y. Seong, “Highly transparent Ag/SnO2 ohmic contact to p-type GaN for ultraviolet light-emitting diodes,” Appl. Phys. Lett. 85(26), 6374–6376 (2004). [CrossRef]

16.

J. H. Son, G. H. Jung, and J.-L. Lee, “Highly reflective Ag-Cu alloy-based ohmic contact on p-type GaN using Ru overlayer,” Opt. Lett. 33(24), 2907–2909 (2008). [CrossRef] [PubMed]

17.

T. B. Massalski and H. Okamoto, Binary Alloy Phase Diagram (ASM International, metal parks, Ohio) (1990).

18.

J.-O. Song, S. Kwak, Y. Park, and T.-Y. Seong, “Improvement of the light output of InGaN-based light-emitting diodes using Cu-doped indium oxide/indium tin oxide p-type electrodes,” Appl. Phys. Lett. 86(21), 213505 (2005). [CrossRef]

19.

R. T. Tung, “Electron transport at metal-semiconductor interfaces: General theory,” Phys. Rev. B Condens. Matter 45(23), 13509–13523 (1992). [CrossRef] [PubMed]

20.

S. K. Lee, C. M. Zettering, M. Ostling, I. Aberg, M. H. Magnusson, K. Deppert, L. E. Wernersson, L. Samuelson, and A. Litwin, “Reduction of the Schottky barrier height on silicon carbide using Au nano-particles,” Solid-State Electron. 46(9), 1433–1440 (2002). [CrossRef]

21.

E. H. Rhoderick and R. H. Williams, Metal-Semiconductor Contacts (Clarendon, Oxford 1988), p. 39.

22.

J. I. Sohn, J.-O. Song, D.-S. Leem, S. Lee, and T.-Y. Seong, “Formation of nonalloyed low resistance Ni/Au ohmic contacts to p-type GaN using Au nano-dots,” Electrochem. Solid-State Lett. 7(9), G179–G181 (2004). [CrossRef]

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(230.4040) Optical devices : Mirrors

ToC Category:
Optical Devices

History
Original Manuscript: September 12, 2013
Revised Manuscript: October 21, 2013
Manuscript Accepted: October 21, 2013
Published: October 29, 2013

Citation
Chang-Hoon Choi, Jaecheon Han, Jae-Seong Park, and Tae-Yeon Seong, "Near ultraviolet InGaN/AlGaN-based light-emitting diodes with highly reflective tin-doped indium oxide/Al-based reflectors," Opt. Express 21, 26774-26779 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-22-26774


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. W. Sun, V. Adivarahan, M. Shatalov, Y. Lee, S. Wu, J. Yang, J. Zhang, and M. A. Khan, “Continuous wave milliwatt power AlGaN light emitting diodes at 280 nm,” Jpn. J. Appl. Phys.43(No. 11A), L1419–L1421 (2004). [CrossRef]
  2. M. Kneissl, Z. Yang, M. Teepe, C. Knollenberg, N. M. Johnson, A. Usikov, and V. Dmitriev, “Ultraviolet InAlGaN light emitting diodes grown on hydride vapor phase epitaxy AlGaN/sapphire templates,” Jpn. J. Appl. Phys.45(5A), 3905–3908 (2006). [CrossRef]
  3. H. Tsuzuki, F. Mori, K. Takeda, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “Novel UV devices on high-quality AlGaN using grooved underlying layer,” J. Cryst. Growth311(10), 2860–2863 (2009). [CrossRef]
  4. J.-O. Song, D.-S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T.-Y. Seong, “Low-resistance and highly-reflective Zn-Ni solid solution/Ag ohmic contacts for flip-chip light-emitting diodes,” Appl. Phys. Lett.83(24), 4990–4992 (2003). [CrossRef]
  5. H. Kim, K. H. Baik, J. Cho, J. W. Lee, S. Yoon, H. Kim, S. N. Lee, C. Sone, Y. Park, and T.-Y. Seong, “High-reflectance and thermally stable AgCu alloy p-type reflectors for GaN-based light-emitting diodes,” IEEE Photon. Technol. Lett.19(5), 336–338 (2007). [CrossRef]
  6. J.-O. Song, J.-S. Ha, and T.-Y. Seong, “Ohmic-contact technology for GaN-based light-emitting diodes: role of P-type contact,” IEEE Trans. Electron. Dev.57(1), 42–59 (2010). [CrossRef]
  7. H. W. Jang and J.-L. Lee, “Mechanism for ohmic contact formation of Ni/Ag contacts on p-type GaN,” Appl. Phys. Lett.85(24), 5920–5922 (2004). [CrossRef]
  8. I.-C. Chen, Y.-D. Chen, C.-C. Hsieh, C.-H. Kuo, and L.-C. Chang, “Highly reflective Ag/La bilayer ohmic contacts to p-type GaN,” J. Electrochem. Soc.158(3), H285–H288 (2011). [CrossRef]
  9. J.-O. Song, W.-G. Hong, J. S. Kwak, Y. Park, and T.-Y. Seong, “Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes,” Appl. Phys. Lett.86(13), 133503 (2005). [CrossRef]
  10. N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett.96(8), 081109 (2010). [CrossRef]
  11. W. H. Lee, D. J. Chae, D. Y. Kim, and T. G. Kim, “Improved electrical and optical properties of vertical GaN LEDs using fluorine-doped ITO/Al ohmic reflectors,” IEEE J. Quantum Electron.47(10), 1277–1282 (2011). [CrossRef]
  12. K. Takehara, K. Takeda, S. Ito, H. Aoshima, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, and H. Amano, “Indium-tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys.51, 042101 (2012). [CrossRef]
  13. B. P. Luther, J. M. DeLucca, S. E. Mohney, and R. F. Karlicek., “Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN,” Appl. Phys. Lett.71(26), 3859–3861 (1997). [CrossRef]
  14. D. L. Hibbard, S. P. Jung, C. Wang, D. Ullery, Y. S. Zhao, H. P. Lee, W. So, and H. Liu, “Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag,” Appl. Phys. Lett.83(2), 311–313 (2003). [CrossRef]
  15. J.-O. Song and T.-Y. Seong, “Highly transparent Ag/SnO2 ohmic contact to p-type GaN for ultraviolet light-emitting diodes,” Appl. Phys. Lett.85(26), 6374–6376 (2004). [CrossRef]
  16. J. H. Son, G. H. Jung, and J.-L. Lee, “Highly reflective Ag-Cu alloy-based ohmic contact on p-type GaN using Ru overlayer,” Opt. Lett.33(24), 2907–2909 (2008). [CrossRef] [PubMed]
  17. T. B. Massalski and H. Okamoto, Binary Alloy Phase Diagram (ASM International, metal parks, Ohio) (1990).
  18. J.-O. Song, S. Kwak, Y. Park, and T.-Y. Seong, “Improvement of the light output of InGaN-based light-emitting diodes using Cu-doped indium oxide/indium tin oxide p-type electrodes,” Appl. Phys. Lett.86(21), 213505 (2005). [CrossRef]
  19. R. T. Tung, “Electron transport at metal-semiconductor interfaces: General theory,” Phys. Rev. B Condens. Matter45(23), 13509–13523 (1992). [CrossRef] [PubMed]
  20. S. K. Lee, C. M. Zettering, M. Ostling, I. Aberg, M. H. Magnusson, K. Deppert, L. E. Wernersson, L. Samuelson, and A. Litwin, “Reduction of the Schottky barrier height on silicon carbide using Au nano-particles,” Solid-State Electron.46(9), 1433–1440 (2002). [CrossRef]
  21. E. H. Rhoderick and R. H. Williams, Metal-Semiconductor Contacts (Clarendon, Oxford 1988), p. 39.
  22. J. I. Sohn, J.-O. Song, D.-S. Leem, S. Lee, and T.-Y. Seong, “Formation of nonalloyed low resistance Ni/Au ohmic contacts to p-type GaN using Au nano-dots,” Electrochem. Solid-State Lett.7(9), G179–G181 (2004). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4 Fig. 5
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited