Abstract
We report in detail the defect dynamics in the active region by monitoring the external quantum efficiency (EQE) - injection current curves, I-V curves, and electroluminescence spectra during the ageing test, under a forward current of 850 mA (85 A/cm2), room temperature. We apply a two-level model to analyze the EQE curves and the electroluminescence spectra. The results suggest that high injection density during the ageing may reduce the density of the Shockley-Reed-Hall nonradiative recombination centers and enhance the carrier mobility and diffusion length. The former effect would directly lead to initial surge of EQE, whereas the latter would enhance the effect of extended defects which leads to reduction in peak EQE and increase in EQE droop rate.
Highlights
Though the GaN-based multiple quantum wells (MQWs) light-emitting diode (LED) have been undergoing a rapid improvement in brightness, as well as external quantum efficiency (EQE), it has two issues remain to be tackled — one is the deceasing in EQE with injection current density (Jf), namely “EQE droop” [1], and the other is the luminous degradation [2]
From the optical power and forward current we are able to calculated the EQE, which is defined as the ratio between the number of photons emitted per second, nhv, and the number of electrons injected into active region per second, ne, by using the Eq (1) below
All the devices exhibited very similar behaviors in optical and electrical parameters. For one of these devices (Device A), the curves of optical power vs. Jf are illustrated in Fig. 1(b) and the EQE curves are shown in Fig. 1(c), which all indicate that the curve is shifting with varying ageing time
Summary
Though the GaN-based multiple quantum wells (MQWs) light-emitting diode (LED) have been undergoing a rapid improvement in brightness, as well as external quantum efficiency (EQE), it has two issues remain to be tackled — one is the deceasing in EQE with injection current density (Jf), namely “EQE droop” [1], and the other is the luminous degradation [2]. That helps us to evaluate the defectdynamics which in turn enriches the theoretical basis of LEDs lifespan prediction for industry needs Because these two topics traditionally were investigated separately, only a few works seen in the literature hitherto focusing on the evolution of the EQE curve with ageing [14,15,16,17]
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