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3 February 2009Reduced non-thermal roll-over in violet-emitting GaInN wide-well LEDs grown on low-dislocation-density substrates
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.1 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 109 cm-2, (b) on low DD GaN templates
on sapphire (DD of 108 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.
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Markus Maier, Thorsten Passow, Michael Kunzer, Wilhelm Schirmacher, Wilfried Pletschen, Lutz Kirste, Klaus Köhler, Joachim Wagner, "Reduced non-thermal roll-over in violet-emitting GaInN wide-well LEDs grown on low-dislocation-density substrates," Proc. SPIE 7231, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XIII, 72310K (3 February 2009); https://doi.org/10.1117/12.819404