Deep Ultraviolet Light Emitting Diodes Based on Short Period Superlattices of AlN/AlGa(In)N

Nikishin, S. A.; Kuryatkov, V.; Chandolu, A.; Borisov, B.; Kipshidze, G.; Ahmad, I.; Holtz, M.; Temkin, H.

doi:10.1143/jjap.42.l1362

Cited by 47 publications

(31 citation statements)

References 16 publications

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“…As current is increased, the latter emissions grow rapidly in intensity while the former saturates. 1,6) The spectrum of the 280 nm LED operated at current density of 250 A/cm 2 is shown in Fig. 10.…”

Section: Optical and Electrical Measurementsmentioning

confidence: 99%

Digital Alloys of AlN/AlGaN for Deep UV Light Emitting Diodes

Nikishin

Holtz

Temkin

2005

Jpn. J. Appl. Phys.

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We report a systematic study of the optical and electrical properties of deep ultraviolet light emitting diodes based on digital alloy structures of AlN/Al0.08Ga0.92N grown by gas source molecular beam epitaxy with ammonia. Digital alloys are formed by short period superlattices consisting of Al0.08Ga0.92N wells, 0.50 or 0.75 nm thick, and AlN barriers, 0.75 to 1.5 nm thick. For digital alloys with effective bandgap of 5.1 eV, average AlN composition 72%, we obtain room temperature electron concentrations up to 1×1019 cm-3 and resistivity of 0.005 Ω·cm and hole concentrations of 1×1018 cm-3 with resistivity of 6 Ω·cm. Light emitting diodes based on digital alloys are demonstrated operating in the range of 250 to 290 nm.

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Section: Optical and Electrical Measurementsmentioning

confidence: 99%

Digital Alloys of AlN/AlGaN for Deep UV Light Emitting Diodes

Nikishin

Holtz

Temkin

2005

Jpn. J. Appl. Phys.

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“…Thus, various methods have been developed, including p-GaN contact layer [117][118][119][120] and superlattice structures, 38,[121][122][123][124][125][126][127][128][129][130] in order to achieve efficient current injection into Al-rich p-Al x Ga 1-x N.…”

Section: 99mentioning

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.

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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...

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“…By optimization of the quality of the AlGaN layers grown over sapphire substrates, several groups have now reported improved LED devices with emission around 280 nm (Yasan et al, 2002;Zhu et al, 2002Zhu et al, , 2003Hanlon et al, 2003). While the majority of the reports described the optimization of AlGaN growth by MOCVD, others have presented the use of MBE with an ammonia source as an alternative approach, along with innovative short-period SL cladding layers (Kipshidze et al, 2001(Kipshidze et al, , 2003Kuryatkov et al, 2003;Nikishin et al, 2003).…”

Section: Deep-uv (Uv-b and Uv-c) Ledsmentioning

confidence: 99%