Impact of active layer design on InGaN radiative recombination coefficient and LED performance
- 15 March 2012
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 111 (6), 063112
- https://doi.org/10.1063/1.3699199
Abstract
The relative roles of radiative and nonradiative processes and the polarization field on the light emission from blue (∼425 nm) InGaN light emitting diodes (LEDs) have been studied. Single and multiple double heterostructure (DH) designs have been investigated with multiple DH structures showing improved efficiencies. Experimental results supported by numerical simulations of injection dependent electron and hole wavefunction overlap and the corresponding radiative recombination coefficients suggest that increasing the effective active region thickness by employing multiple InGaN DH structures separated by thin and low barriers is promising for LEDs with high efficiency retention at high injection. The use of thin and low barriers is crucial to enhance carrier transport across the active region. Although increasing the single DH thickness from 3 to 6 nm improves the peak external quantum efficiency (EQE) by nearly 3.6 times due to increased density of states and increased emitting volume, the internal quantum efficiency (IQE) suffers a loss of nearly 30%. A further increase in the DH thickness to 9 and 11 nm results in a significantly slower rate of increase of EQE with current injection and lower peak EQE values presumably due to degradation of the InGaN material quality and reduced electron-hole spatial overlap. Increasing the number of 3 nm DH active regions separated by thin (3 nm) In0.06Ga0.94N barriers improves EQE, while maintaining high IQE (above 95% at a carrier concentration of 1018 cm−3) and showing negligible EQE degradation up to 550 A/cm2 in 400 × 400 μm2 devices due to increased emitting volume and high radiative recombination coefficients and high IQE. Time-resolved photoluminescence measurements revealed higher radiative recombination rates with increasing excitation due to screening of the internal field and enhanced electron and hole overlap at higher injection levels. To shed light on the experimental observations, the effect of free-carrier screening on the polarization field at different injection levels and the resulting impact on the quantum efficiency were investigated by numerical simulations.Keywords
This publication has 26 references indexed in Scilit:
- On the quantum efficiency of InGaN light emitting diodes: Effects of active layer design, electron cooler, and electron blocking layerPhysica Status Solidi (a), 2011
- Internal quantum efficiency and nonradiative recombination coefficient of GaInN/GaN multiple quantum wells with different dislocation densitiesApplied Physics Letters, 2009
- Carrier distribution in (0001)InGaN∕GaN multiple quantum well light-emitting diodesApplied Physics Letters, 2008
- Origin of efficiency droop in GaN-based light-emitting diodesApplied Physics Letters, 2007
- Pyroelectric properties of Al(In)GaN/GaN hetero- and quantum well structuresJournal of Physics: Condensed Matter, 2002
- Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structuresApplied Physics Letters, 1999
- InGaN/GaN quantum wells studied by high pressure, variable temperature, and excitation power spectroscopyApplied Physics Letters, 1998
- Effects of Piezoelectric Fields in GaInN/GaN and GaN/AlGaN Heterostructures and Quantum WellsMRS Proceedings, 1997
- Radiative recombination lifetime measurements of InGaN single quantum wellApplied Physics Letters, 1996
- Electro-optic properties of the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylateApplied Physics Letters, 1996