Abstract
The Purcell effect in GaN-based flip-chip (FC) light-emitting diode (LED) structures is investigated numerically using finite-difference time-domain simulations. Depending on the thickness of the p-GaN layer, the variation of the Purcell factor of FC LEDs is obtained to be as high as 20%, which results in the relative modification of the internal quantum efficiency (IQE) as large as 8% and 2.5% for the unmodified IQE of 0.4 and 0.8, respectively. Since the influence of the Purcell effect becomes more conspicuous as the IQE decreases, the Purcell enhancement can be advantageously used to mitigate the efficiency droop problem to some extent. When the Purcell effect is positively applied to the blue LED with the peak IQE of 0.8 and the droop ratio of 29.1%, the peak IQE and the droop ratio are found to be improved to 0.82 and 26.3%. This small but non-negligible effect on IQE is expected to be importantly adopted for industry development of high efficiency LEDs.
Highlights
Over the last decade, there has been remarkable progress in the development of highefficiency blue light-emitting diodes (LEDs) based on InGaN/GaN materials for general lighting applications [1,2,3]
3.1 Simulation of the Purcell factor In Fig. 2, FP for the FC and the epi-up LED structures is plotted as a function of the p-GaN thickness
Since the Purcell effect results from the self-interference effect of light emitted from the quantum wells (QWs) due to reflection from the reflecting surface, FP varies periodically with the pGaN thickness [22,23,24]
Summary
There has been remarkable progress in the development of highefficiency blue light-emitting diodes (LEDs) based on InGaN/GaN materials for general lighting applications [1,2,3]. GaN-based LEDs suffer from a phenomenon commonly referred to as “efficiency droop” [4,5,6]. The internal quantum efficiency (IQE) of LEDs typically peaks at a few A/cm and droops with increasing current density. Most works for mitigating the efficiency droop have focused on reducing the nonradiative recombination
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