Abstract
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 <i>k ⋅ p</i> 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<sub>0.28</sub>Ga<sub>0.72</sub>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<sub>x</sub>Ga<sub>1-x</sub>N, lattice-matched
Al<sub>x</sub>In<sub>1-x</sub>N, and lattice-matched
Al<sub>x</sub>Ga<sub>1-x-y</sub>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.
© 2013 IEEE
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