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Reducing the efficiency droop by lateral carrier confinement in InGaN/GaN quantum-well nanorods

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Abstract

Efficiency droop is a major obstacle facing high-power application of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs). In this paper, we report the suppression of efficiency droop induced by the process of density-activated defect recombination in nanorod structures of a-plane InGaN/GaN QWs. In the high carrier density regime, the retained emission efficiency in a dry-etched nanorod sample is observed to be over two times higher than that in its parent QW sample. We further argue that such improvement is a net effect that the lateral carrier confinement overcomes the increased surface trapping introduced during fabrication.

© 2014 Optical Society of America

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Figures (5)

Fig. 1
Fig. 1 Lateral carrier confinement in QW nanorods. (a) Schematic sketch of the impact of lateral carrier confinement on the process of DADR (not in scale). (b) A SEM image of the nanorod sample. The average radius is ~130 nm.
Fig. 2
Fig. 2 Reduced efficiency droop in the nanorod sample. (a) The normalized QW emission intensity per unit excitation power (logarithm scale) and (b) intensity ratio between the defect emission and QW emission are plotted versus excitation fluence. The data from the nanorod sample and the parent QW sample are compared. (c) PL emission spectra from the nanorod sample recorded under different excitation fluences. The dashed line indicates the fluence-dependent shift of the emission peak.
Fig. 3
Fig. 3 Time-integrated PL spectra from the nanorod sample and the parent QW sample recorded under the same excitation fluence at ~15 μJ/cm2.
Fig. 4
Fig. 4 Transient optical evidence of lateral carrier confinement in nanorods. Normalized TRPL spectra recorded at the center wavelength of QW emission from (a) the nanorod sample and (b) the QW sample are shown in comparison with the profile of instrumental response function (IRF). Following the initial abrupt rise, the curves recorded from both samples exhibit a delayed-rise component. The amplitude (D) of delayed-rise component is marked from the kink point of the rising edge in the TRPL spectra. The red dashed lines are the curves fitting to single-exponential decay functions.
Fig. 5
Fig. 5 Control experiments on the surface trapping effect. Time-resolved (a) and time-integrated (a, inset) PL spectra of three control samples (the c-plane QWs (c-MQW), as-etched QW nanorods (c-NR), and surface-passivated QW nanorods (c-NR-S) recorded under the same conditions are compared. The dashed line highlights the ultrafast decay component. (b) The normalized QW emission intensities per unit excitation power from the three samples are compared as a function of the excitation fluence.
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