Origin of the injection-dependent emission blueshift and linewidth broadening of III-nitride light-emitting diodes (original) (raw)
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Modeling of color-coded III-nitride LED structures with deep quantum wells
Optical and Quantum Electronics, 2013
We present, to the best of our knowledge, the first successful simulation of color-coded IIInitride light-emitting diodes (LEDs) incorporating in their active regions shallow and deep InGaN quantum wells (QWs). Dichromatic violet-aquamarine semipolar LEDs grown in Ga-polar and N-polar crystallographic orientations (Y. Kawaguchi et.al., APL 100, 231110, 2012) were used as an experimental benchmark. Opposite interface polarization charges in Ga-polar and N-polar LEDs provide different conditions for carrier transport and account for different shape of color-coded emission spectra. To reproduce experimentally observed trends, several effects specific for deep III-nitride QWs were essential in our modeling including (i) strongly non-equilibrium character of active QW populations, (ii) dynamic carrier overshoot of narrow QW layers, and (iii) Auger-assisted QW depopulation.
Carrier injection and light emission in visible and UV nitride LEDs by modeling
physica status solidi (b), 2004
Polarization effects on carrier injection and light emission are considered by modeling with reference to single-quantum-well blue light emitting diode heterostructures of either Ga-or N-polarity. The model accounts for specific features of nitride semiconductors, spontaneous and piezo-polarization, strong nonradiative recombination on threading dislocation cores, complex valence band structure, etc., and allows detailed analysis of the device operation. The modeling results are compared with available observations.
Modeling of III-Nitride Multiple-Quantum-Well Light-Emitting Structures
IEEE Journal of Selected Topics in Quantum Electronics, 2000
Spatial inhomogeneity of carrier injection across the multiple quantum well (MQW) active region of a semiconductor light emitter can impose severe limitations on the device efficiency. In III-nitride based devices, the large disparity of electron and hole transport and the excessive depth of active QWs trigger the process of inhomogeneous QW injection which is further aggravated by strong dependence of QW radiative characteristics on the QW injection conditions due to (i) intra-QW screening of polarization fields in polar and semipolar materials, (ii) phase-space filling effect in lowest QW subbands at higher levels of carrier injection, and (iii) exceedingly nonequilibrium character of the electron and hole populations in deep QWs. All these tendencies become more pronounced in longer-wavelength emitters. The residual QW charges provide strong feedback to the QW injection conditions thus requiring a high level of self-consistency between the active region transport simulation and the QW emission modeling.
Journal of Applied Physics, 2012
Strong disparity of electron and hole transport in III-nitride materials is commonly accepted as a main reason for inhomogeneous carrier injection in multiple-quantum well (MQW) active regions of light emitters operating in visible spectral range. In this work, we show that two more factors, specifically (i) excessive depth of III-nitride QWs and (ii) strongly non-equilibrium character of electron and hole populations in optically active QW, are responsible for the active region inhomogeneity in GaN-based light emitters. Modeling shows that electron and hole populations of deep III-nitride QWs are highly imbalanced and substantially deviate from thermodynamic equilibrium with corresponding mobile carrier subsystems in the device active region. In turn, large residual QW charges provide strong impact on the active region electrical uniformity and QW injection conditions. We demonstrate that, as a result of non-equilibrium effects in QW population, even nonpolar III-nitride light emitters with deep QWs suffer from inhomogeneous carrier injection, large QW residual charges, and overall electrical non-uniformity of MQW active regions. V C 2012 American Institute of Physics. [http://dx.
Physical Review Materials, 2020
The presence of alloy disorder in III-nitride materials has been demonstrated to play a significant role in device performance through effects such as carrier localization and carrier transport. Relative to blue light emitting diodes (LEDs), these effects become more severe at green wavelengths. Because of the potential fluctuations that arise due to alloy disorder, full three-dimensional (3D) simulations are necessary to accurately relate materials properties to device performance. We demonstrate experimentally and through simulation that increased quantum well (QW) number in c-plane green LEDs contributes to excess driving voltage, and therefore reduced electrical efficiency. Experimentally, we grew an LED series with the number of QWs varying from one to seven and observed a systematic increase in voltage with the addition of each QW. Trends in LED electrical properties obtained from 3D simulations, which account for the effects of random alloy fluctuations, are in agreement with experimental data. Agreement is achieved without the need for adjusting polarization parameters from their known values. From these results, we propose that the polarization induced barriers at the GaN/InGaN (lower barrier/QW) interfaces and the sequential filling of QWs both contribute significantly to the excess forward voltage in multiple QW c-plane green LEDs.
Inhomogeneous injection in III-nitride light emitters with deep multiple quantum wells
Journal of Computational Electronics, 2015
Excessive depth of optically active quantum wells (QWs) and related increase in QW population capacity is one of the main causes of inhomogeneous carrier injection and unequal QW populations in multiple-quantum-well (MQW) III-nitride light emitters operating in the visible range. In turn, uneven distribution of injected carriers across the device's active region creates imbalance between confined electron and hole QW populations and supports large residual QW charges, especially in marginally located n-side and p-side QWs. QW charges are strongly non-equilibrium as determined by dynamic balance between carrier capture and recombination rates, with the later being progressively faster in excessively deep QWs.
Physics and Simulation of Optoelectronic Devices XX, 2012
III-nitride visible light emitters employ deep QWs and feature strong disparity of electron and hole transport in diode structures. As a result, multi-QW active regions of such devices suffer from inhomogeneous carrier injection, large residual charges of active QWs, and overall active region electrical non-uniformity which unfavorably affects the emitter efficiency. In this work, we show that electron and hole populations of deep optically active III-nitride QWs are highly imbalanced and substantially deviate from thermodynamic equilibrium with corresponding mobile carrier subsystems. Non-equilibrium QW populations are self-consistently determined by carrier injection and light generation processes in active QWs. In turn, QW residual charges impose strong feedback on the active region electrical uniformity. Our selfconsistent modeling of QW radiative characteristics and multi-QW carrier transport in diode structures relates the effects of non-equilibrium QW populations, inhomogeneous QW injection and residual QW charges to the structure internal efficiency. Comparative modeling of polar and nonpolar diodes shows that in both types of structures the nonequilibrium effects tend to decrease the QW operational electron populations; this trend benefits the active region electrical uniformity. For device simulation, we use COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc.
Journal of Display Technology
Current injection efficiency and internal quantum efficiency (IQE) in InGaN quantum well (QW) based light emitting diodes (LEDs) are investigated. The analysis is based on current continuity relation for drift and diffusion carrier transport across the QW-barrier systems. A self-consistent 6-band method is used to calculate the band structure for InGaN QW structure. Carrier-photon rate equations are utilized to describe radiative and non-radiative recombination in the QW and the barrier regions, carrier transport and capture time, and thermionic emission leading to carrier leakage out of the QW. Our model indicates that the IQE in the conventional 24-Å In Ga N-GaN QW structure reaches its peak at low injection current density and reduces gradually with further increase in current due to the large thermionic carrier leakage. The efficiency droop phenomenon at high current density in III-nitride LEDs is thus consistent with the high-driving-current induced quenching in current injection efficiency predicted by our model. The effects of the monomolecular recombination coefficient, Auger recombination coefficient and GaN hole mobility on the current injection efficiency and IQE are studied. Structures combining InGaN QW with thin larger energy bandgap barriers such as Al Ga N, lattice-matched Al In N, and lattice-matched Al In Ga N have been analyzed to improve current injection efficiency and thus minimize droop at high current injection in III-nitride LEDs. Effect of the thickness of the larger energy bandgap barriers (AlGaN, AlInN and AlInGaN) on injection efficiency and IQE are investigated. The use of thin AlGaN barriers shows slight reduction of quenching of the injection efficiency as the current density increases. The use of thin lattice-matched AlInN or AlInGaN barriers shows significant suppression of efficiency-droop in nitride LEDs.
COMSOL-based Ostendo's Opto-electronic Device Modeling Software (ODMS) has been updated to include effects of non-equilibrium QW populations in semiconductor light-emitting and laser diodes. III-nitride light emitters with different levels of polarity have been compared as an illustrative example of ODMS performance. Modeling proved that high intra-QW recombination rates in III-nitride light emitters make the QW populations strongly non-equilibrium and vulnerable to inhomogeneous injection in multiple-QW devices. QW popu-lations are further affected by disparate electron and hole transport across the active region.