Mingoo Kang

Dependence of efficiencies in GaN-based vertical blue light-emitting diodes on the thickness and doping concentration of the n-GaN layer.

We investigate the dependence of various efficiencies in GaN-based vertical blue light-emitting diode (LED) structures on the thickness and doping concentration of the n-GaN layer by using numerical simulations. The electrical efficiency (EE) and the internal quantum efficiency (IQE) are found to increase as the thickness or doping concentration increases due to the improvement of current spreading. On the contrary, the light extraction efficiency (LEE) decreases with increasing doping concentration or n-GaN thickness by the free-carrier absorption. By combining the results of EE, IQE, and LEE, wall-plug efficiency (WPE) of the vertical LED is calculated, and the optimum thickness and doping concentration of the n-GaN layer is found for obtaining the maximum WPE.

Analysis of below-threshold efficiency characteristics of InGaN-based blue laser diodes

In this study, we investigate the below-threshold emission characteristics of InGaN-based blue laser diodes (LDs) emitting at 442 nm to study the efficiency droop effects in InGaN LDs. From the measurement of spontaneous emission in the LD, it is observed that the peak efficiency appears at a current density of ∼20 A/cm2 and the efficiency at the threshold current density of ∼2.3 kA/cm2 are reduced to ∼47% of the peak efficiency. The measured spontaneous emission characteristics are analyzed using the carrier rate equation model, and the peak internal quantum efficiency is found to be ∼75% using the fit of the measured efficiency curve. In addition, the Auger recombination coefficient of the measured InGaN blue LD is found to be 10−31–10−30 cm6/s, which is somewhat lower than that reported for InGaN-based blue light-emitting diodes. It is discussed that low dislocation density and uniform current injection in quantum wells may have resulted in the low Auger recombination coefficient of InGaN LDs.