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Electrical and optical characteristics of highly transparent MOVPE-grown AlGaN-based tunnel heterojunction LEDs emitting at 232 nm

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Photonics Research 2021年第6期9卷 1117-1123页

作者： FRANK MEHNKE CHRISTIAN KUHN martin guttmann LUCA SULMONI VERENA MONTAG JOHANNES GLAAB TIM WERNICKE MICHAEL KNEISSL Institute of Solid State Physics Technische Universität Berlin10623 BerlinGermany Ferdinand-Braun-Institut Leibniz-Institut für Höchstfrequenztechnik12489 BerlinGermany Current address:School of Electrical and Computer Engineering Georgia Institute of TechnologyAtlantaGeorgia 30332USA

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 *** 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 *** 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.

关键词： heterojunction MOVPE AlGaN

Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire

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Photonics Research 2020年第4期8卷 589-594页

作者： 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 Institute of Solid State Physics Technische Universitat BerlinHardenbergstraβe 3610623 BerlinGermany Ferdinand-Braun-Institut Leibniz-Institut für HochstfrequenztechnikGustav-Kirchhoff-Strafβe 412489 BerlinGermany Leibniz-Institut für Kristallzüchtung Max-Born-Strafβe 212489 BerlinGermany

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 *** 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 *** 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 *** 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),***,Monte Carlo ray-tracing simulations showed a 15%increase in light-extraction efficiency due to the voids formed in the ELO *** 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.

关键词： Improved performance UVC-LEDs combination high-temperature annealing epitaxially laterally overgrown AlN/sapphire AlN UVC

Recombination mechanisms and thermal droop in AlGaN-based UV-B LEDs

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Photonics Research 2017年第2期5卷 44-51页

作者： 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 Department of Information Engineering University of Padova Ferdinand-Braun-Institut Leibniz-Institut fur Hochstfrequenztechnik Technische Universitat Berlin Institut für Festkorperphysik

This paper reports a comprehensive analysis of the origin of the electroluminescence(EL)peaks and of the thermal droop in UV-B AlGaN-based *** 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 *** 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.

关键词： Recombination mechanisms and thermal droop in AlGaN-based UV-B LEDs Ga AlGaN EBL SRH UV

MOVPE-grown AlGaN-based tunnel heterojunctions enabling fully transparent UVC LEDs

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Photonics Research 2019年第5期7卷 I0008-I0012页

作者： Christian Kuhn Luca Sulmoni martin guttmann Johannes Glaab Norman Susilo Tim Wernicke Markus Weyers Michael Kneissl Technische Universitat Berlin Institute of Solid State Physics Hardenbergstr. 36 EW6-1 10623 Berlin Germany Ferdinand-Braun-Institut Leibniz-Institut fur Hochstfrequenztechnik Gustav-Kirchhoff-Str. 4 12489 Berlin Germany

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 ***, 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.

关键词： MOVPE-grown AlGaN-based UVC LEDs