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Reduced non-thermal roll-over in violet-emitting GaInN wide-well LEDs grown on low-dislocation-density substrates

: Maier, M.; Passow, T.; Kunzer, M.; Schirmacher, W.; Pletschen, W.; Kirste, L.; Köhler, K.; Wagner, J.


Streubel, K.P. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Light-emitting diodes: Materials, devices, and applications for solid state lighting XIII : 27 - 29 January 2009, San Jose, California, United States
Bellingham, WA: SPIE, 2009 (Proceedings of SPIE 7231)
ISBN: 978-0-8194-7477-3
Paper 72310K
Conference "Light-Emitting Diodes - Materials, Devices, and Applications for Solid State Lighting" <8, 2009, San Jose/Calif.>
Fraunhofer IAF ()

Near-UV LEDs emitting at around 400 nm can be used e.g. as pump light source in tri-phosphor RGB white luminescence-conversion LEDs with high color rendering. Although non-thermal roll-over decreases towards shorter emission wavelengths in GaInN-based LEDs, this effect still limits the efficiency of 400 nm emitting LEDs at current densities above 50 A/cm2. One way to overcome non-thermal roll-over is to combine a GaInN wide-well active region with the growth on low dislocation density (DD) substrates. Single-well LEDs with GaInN layer widths between 3 nm and 18 nm were grown (a) directly on sapphire substrates with a resulting DD of 10(exp 9) cm-2, (b) on low DD GaN templates on sapphire (DD of 10(exp 8) cm-2), and (c) on freestanding GaN substrates (FS-GaN, DD of 4×107 cm-2). At low current densities (pulsed mode operation) the LEDs with a 3 nm GaInN QW active region showed the highest efficiency, irrespective of the substrate. However, the electroluminescence (EL) efficiency peaks at around 50 A/cm2 and shows a clear non-thermal roll-over towards higher current densities. The efficiency of LEDs with well widths >3 nm grown on sapphire decreases with increasing well width over the whole range of current densities (<=300 A/cm2). However, when grown on low DD GaN templates or FS-GaN, the efficiency of the LEDs with 11 and 18 nm wide GaInN layers surpasses that of the conventional LEDs (well widths <=6 nm) for current densities >=250 A/cm2, yielding the highest EL efficiency of all LED-structures.