Improved External Efficiency InGaN-Based Light-Emitting Diodes with Transparent Conductive Ga-Doped ZnO as p-Electrodes

Nakahara, Ken; Tamura, Kentaro; Sakai, Mitsuhiko; Nakagawa, Daisuke; Ito, Norikazu; Sonobe, Masayuki; Takasu, H.; Tampo, Hitoshi; Fons, Paul; Matsubara, Koji; Iwata, K.; Yamada, A.; Niki, Shigeru

doi:10.1143/jjap.43.l180

Cited by 61 publications

(28 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[50][51][52][53][54] However, TCO-based TCEs with desired electrical resistance have fairly low transmittances in the UV spectrum. Thus, to enhance both the UV transmittance and the electrical properties of TCEs, various approaches, including metal-doped TCOs, [55][56][57][58][59][60] oxide/metal/oxide structure, 61 and surface treatments, 62,63 have been investigated. Metal-doped TCOs, such as Sb-doped tin oxide (ATO), 56 Gadoped ZnO (GZO), 59 Al-doped ZnO (AZO), 60 and Ti-, Al-, Ga-, and Ge-doped ITO, 57,58 have been investigated as a candidate for near UV (NUV) p-type TCEs because of their reasonable electrical resistance and high optical transmittance in the NUV spectrum.…”

Section: Ohmic Contacts To P-gan For Near Uv Ledsmentioning

confidence: 99%

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Park

Kim

Cho

et al. 2017

ECS J. Solid State Sci. Technol.

View full text Add to dashboard Cite

There is a rapidly growing demand for highly efficient ultraviolet (UV) light sources for a wide variety of applications. In particular, state-of-the-art AlGaN deep UV light-emitting diodes (DUV LEDs) exhibit inadequately low external quantum efficiencies (EQEs). The low efficiencies are attributed to the inherent material properties of high-Al-content AlGaN including strained epitaxial layers, low carrier concentrations, and strong transverse magnetic (TM)-polarized light emission. Extensive efforts have been made to tackle these challenging issues and technological developments have been achieved and enabled the fabrication of reasonable EQE LEDs. In this review, recent advances in the growth of high-quality AlGaN epitaxial layers, transparent and reflective ohmic contacts, and light extraction for AlGaN-based UV LEDs are reviewed. Al x Ga 1-x N-based ultraviolet light-emitting diodes (UV LEDs) are of technological importance because of their applications in numerous areas such as water purification, biological analysis, sensing, epoxy curing, high-density optical storage, white light illumination, UV adhesives, 3-dimensional (3D) printer and UV-coating.1,2 These applications are made possible because of their wide bandgap energy range in the UV spectrum, which spans from 6.2 eV (AlN) to 3.4 eV (GaN), namely, from UV-A (320-400 nm), UV-B (290-320 nm) to UV-C (200-290 nm).3-7 The external quantum efficiency (EQE) of Al x Ga 1-x N-based UV LEDs decreases rapidly as the molar fraction (x) of Al increases, namely, as the wavelength decreases, as illustrated in Figure 1. 8 Thus, a great deal of effort has been made in order to improve the EQE of UV LEDs. The effort notwithstanding, however, the EQE of AlGaN-based UV LEDs is still insufficiently low. The typical EQE of UV LEDs, specifically in the UV-C spectral range (100-280 nm), is less than 5% and decreases down to 10 -6 % for 210-nm AlN-based UV LEDs. 4 These low EQEs are associated with the intrinsic material properties of Al x Ga 1-x N.1,2 Figure 2 exhibits a schematic diagram of a typical AlGaN UV LED structure grown on a sapphire substrate. The structure consists of a Si-doped n-type AlGaN, an Al x Ga 1-x N/Al y Ga 1-y N multiple-quantum well (MQW) active region, an AlGaN-based electron-blocking layer (EBL), a Mg-doped p-type AlGaN, and a Mg-doped p-type GaN. Almost every layer in the structure poses different technical issues, which limit the efficiency of UV LEDs, as shown in Figure 2. First, increasing the Al content generally results in a poor crystallinity of AlGaN epilayers, causing a poor internal quantum efficiency (IQE). Second, both n-type and ptype doping efficiencies of AlGaN are difficult to increase because the ionization energies of acceptor (Mg) and donor (Si) dopants largely increase with increasing Al content. The low doping efficiency causes several technological problems: (i) a poor electrical efficiency (EE) attributable to high-resistance contacts on resistive n-type and p-type AlGaN; (ii) current crowding causing non-uniform current in...

show abstract

Section: Ohmic Contacts To P-gan For Near Uv Ledsmentioning

confidence: 99%

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Park

Kim

Cho

et al. 2017

ECS J. Solid State Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…The uses of ZnO-based materials as alternative TCOs are expanding to flat panel displays [1], light emitting diodes [2] and solar cells [3]. High crystalline quality is not always a requirement for TCO applications, but the need for compatibility with established fabrication processes should be emphasized.…”

Section: Introductionmentioning

confidence: 99%

Halide vapor phase epitaxy of ZnO studied by thermodynamic analysis and growth experiments

Fujii

Yoshii²,

Kumagai

et al. 2011

Journal of Crystal Growth

View full text Add to dashboard Cite

“…4 Furthermore, it has been reported that a Ga-doped ZnO transparent conductive oxide layer contacting to p-GaN results in a twofold higher brightness in GaN UV LEDs, in comparison to the conventional Ni/Au p-contacts. 5 Semiconductor nanowires have attracted extensive attention due to their dramatically enhanced electron-hole interaction from a reduced dimensionality. ZnO one-dimensional (1-D) nanostructures have been grown on various substrates including Si, glass, and c-sapphire at low temperature (~400°C) by metalorganic chemical vapor deposition (MOCVD) via a catalyst-free self-nucleation growth.…”

Section: Introductionmentioning

confidence: 99%

Structural and Optical Properties of ZnO Nanotips Grown on GaN Using Metalorganic Chemical Vapor Deposition

Zhong

Saraf

Chen

et al. 2007

Journal of Elec Materi

View full text Add to dashboard Cite

ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction (XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO| |(0002)GaN and (10 " 10)ZnO| |(10 " 10)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are 11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni's equation to study the variation of energy bandgap versus temperature.

show abstract

Improved External Efficiency InGaN-Based Light-Emitting Diodes with Transparent Conductive Ga-Doped ZnO as p-Electrodes

Cited by 61 publications

References 11 publications

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Halide vapor phase epitaxy of ZnO studied by thermodynamic analysis and growth experiments

Structural and Optical Properties of ZnO Nanotips Grown on GaN Using Metalorganic Chemical Vapor Deposition

Contact Info

Product

Resources

About