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| 1 | Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire显示文摘We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes(UV-LEDs)emitting at 265 nm grown on stripe-patterned high-temperature annealed(HTA)epitaxially laterally overgrown(ELO)aluminium nitride(AIN)/sapphire templates.For this purpose,the structural and electro-optical properties of ultraviolet-c light-emitting diodes(UVC-LEDs)on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared.Cathodoluminescence measurements reveal dark spot densities of 3.5×10^9 cm^-2,1.1×10^9 cm^-2,1.4×10^9 cm^-2,and 0.9×10^9 cm^-2 in multiple quantum well samples on as-grown planar AIN/sapphire,HTA planar AlN/sapphire,ELO AlN/sapphire,and HTA ELO AlN/sapphire,respectively,and are consistent with the threading dislocation densities determined by transmission electron microscopy(TEM)and high-resolution X-ray diffraction rocking curve.The UVC-LED performance improves with the reduction of the threading dislocation densities(TDDs).The output powers(measured on-wafer in cw operation at 20 mA)of the UV-LEDs emitting at 265 nm were 0.03 mW(planar AlN/sapphire),0.8 mW(planar HTA AlN/sapphire),0.9 mW(ELO AlN/sapphire),and 1.1 mW(HTA ELO AlN/sapphire),respectively.Furthermore,Monte Carlo ray-tracing simulations showed a 15%increase in light-extraction efficiency due to the voids formed in the ELO process.These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs,improving both the internal quantum efficiency and the light-extraction efficiency. | NORMAN SUSILO EVIATHAR ZIFFER SYLVIA HAGEDORN LEONARDO CANCELLARA CARSTEN NETZEL NEYSHA LOBO PLOCH SHAOJUN WU JENS RASS SEBASTIAN WALDE LUCA SULMONI MARTIN GUTTMANN TIM WERNICKE MARTIN ALBRECHT MARKUS WEYERS MICHAEL KNEISSL | 2020 | Photonics Research2020，8，4： | 4 |
| 2 | Electrical properties and microstructure formation of V/Al-based n-contacts on high Al mole fraction n-AlGaN layers显示文摘The electrical and structural properties of V/Al-based n-contacts on n‐AlxGa1−xN with an Al mole fraction x ranging from x=0.75 to x=0.95 are investigated.Ohmic n-contacts are obtained up to x=0.75 with a contact resistivity of 5.7×10^−4Ω·cm^2 whereas for higher Al mole fraction the IV characteristics are rectifying.Transmission electron microscopy reveals a thin crystalline AlN layer formed at the metal/semiconductor interface upon thermal annealing.Compositional analysis confirmed an Al enrichment at the interface.The interfacial nitride-based layer in n-contacts on n‐Al0.9Ga0.1N is partly amorphous and heavily contaminated by oxygen.The role and resulting limitations of Al in the metal stack for n-contacts on n-AlGaN with very high Al mole fraction are discussed.Finally,ultraviolet C(UVC)LEDs grown on n‐Al0.87Ga0.13N and emitting at 232 nm are fabricated with an operating voltage of 7.3 V and an emission power of 120μW at 20 mA in cw operation. | LUCA SULMONI FRANK MEHNKE ANNA MOGILATENKO MARTIN GUTTMANN TIM WERNICKE MICHAEL KNEISSL | 2020 | Photonics Research2020，8，8： | 4 |
| 3 | Recombination mechanisms and thermal droop in AlGaN-based UV-B LEDs显示文摘This paper reports a comprehensive analysis of the origin of the electroluminescence(EL)peaks and of the thermal droop in UV-B AlGaN-based LEDs.By carrying out spectral measurements at several temperatures and currents,(i)we extract information on the physical origin of the various spectral bands,and(ii) we develop a novel closed-form model based on the Shockley–Read–Hall theory and on the ABC rate equation that is able to reproduce the experimental data on thermal droop caused by non-radiative recombination through deep levels.In the samples under test,the three EL bands are ascribed to the following processes:band-to-band recombination in the quantum wells(main EL peak),a parasitic intra-bandgap radiative transition in the quantum well barriers,and a second defect-related radiative process in the p-AlGaN superlattice. | CARLO DE SANTI MATTEO MENEGHINI DESIREE MONTI JOHANNES GLAAB MARTIN GUTTMANN JENS RASS SVEN EINFELDT FRANK MEHNKE JOHANNES ENSLIN TIM WERNICKE MICHAEL KNEISSL GAUDENZIO MENEGHESSO ENRICO ZANONI | 2017 | Photonics Research2017，5，2： | 2 |
| 4 | MOVPE-grown AlGaN-based tunnel heterojunctions enabling fully transparent UVC LEDs显示文摘We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characteristics can be improved by exploiting the higher conductivity of n-AlGaN layers as well as a lower resistance of n-contacts. UVC LEDs with AlGaN:Mg/AlGaN:Si tunnel junctions exhibiting single peak emission at268 nm have been realized, demonstrating effective carrier injection into the AlGaN multiple quantum well active region. The incorporation of a low band gap interlayer enables effective tunneling and strong voltage reduction.Therefore, the interlayer thickness is systematically varied. Tunnel heterojunction LEDs with an 8 nm thick GaN interlayer exhibit continuous-wave emission powers >3 m W near thermal rollover. External quantum efficiencies of 1.4% at a DC current of 5 m A and operating voltages of 20 V are measured on-wafer. Laterally homogeneous emission is demonstrated by UV-sensitive electroluminescence microscopy images. The complete UVC LED heterostructure is grown in a single epitaxy process including in situ activation of the magnesium acceptors. | Christian Kuhn Luca Sulmoni Martin Guttmann Johannes Glaab Norman Susilo Tim Wernicke Markus Weyers Michael Kneissl | 2019 | Photonics Research2019，7，5： | 1 |
| 5 | Electrical and optical characteristics of highly transparent MOVPE-grown AlGaN-based tunnel heterojunction LEDs emitting at 232 nm显示文摘We present the growth and electro-optical characteristics of highly transparent AlGaN-based tunnel heterojunction light-emitting diodes(LEDs)emitting at 232 nm entirely grown by metalorganic vapor phase epitaxy(MOVPE).A GaN:Si interlayer was embedded into a highly Mg-and Si-doped Al_(0.87)Ga_(0.13)N tunnel junction to enable polarization field enhanced tunneling.The LEDs exhibit an on-wafer integrated emission power of 77μWat 5 mA,which correlates to an external quantum efficiency(EQE)of 0.29%with 45μWemitted through the bottom sapphire substrate and 32μW emitted through the transparent top surface.After depositing a highly reflective aluminum reflector,a maximum emission power of 1.73 mW was achieved at 100 mA under pulsed mode operation with a maximum EQE of 0.35%as collected through the bottom substrate. | FRANK MEHNKE CHRISTIAN KUHN MARTIN GUTTMANN LUCA SULMONI VERENA MONTAG JOHANNES GLAAB TIM WERNICKE MICHAEL KNEISSL | 2021 | Photonics Research2021，9，6： | 0 |
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