The reverse leakage characteristics of AlGaNbased ultraviolet light-emitting diodes fabricated on sapphire substrate are studied by temperature-variable current–voltage(I–V)measurement from 300 to 450 K.At low-reverse bias range(0–0.5 V),the reverse leakage current exhibits tunneling characteristics.Meanwhile,under a more negative reverse bias range([0.5 V),the log(I)–log(V)plots exhibit close-to-linear dependency,which is in good agreement with the transport mechanism of space-charge limited current.A phenomenological leakage current model focusing on electron transmission primarily through continuous defect band formed by linear defects like dislocations is suggested to explain the reverse current–voltage characteristics.
Rong JiangDawei YanHai LuRong ZhangDunjun ChenYoudou Zheng
The efficiency droop behaviors of GaN-based green light-emitting diodes （LEDs） are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level （1 A/cm2 ） with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs.
