"U-Turn" Feature In The Efficiency-Versus-Current Curve Of Gainn/Gan Light-Emitting Diodes

The onset of the efficiency droop in GaInN/GaN blue light-emitting diodes (LEDs), i.e., the maximum-efficiency point, typically occurs at current densities of 1-10 A/cm(2) and the efficiency decreases monotonically beyond the onset. At typical operating current densities (10-100 A/cm(2)), LEDs are strongly affected by the droop. At cryogenic temperatures, an increase in the efficiency, i.e., a "U-turn" feature, is found in the droop regime of the efficiency-versus-current curve. The occurrence of the U-turn feature coincides with a distinct increase in device conductivity, which is attributed to an enhancement in p-type conductivity that in turn increases the injection efficiency. (c) 2014 AIP Publishing LLC.