Development of high performance green c-plane III-nitride light-emitting diodes

The effect of employing an AlGaN cap layer in the active region of green c-plane light-emitting diodes (LEDs) was studied. Each quantum well (QW) and barrier in the active region consisted of an InGaN QW and a thin Al_0.30Ga_0.70N cap layer grown at a relatively low temperature and a GaN barrier grown at a higher temperature. A series of experiments and simulations were carried out to explore the effects of varying the Al_0.30Ga_0.70N cap layer thickness and GaN barrier growth temperature on LED efficiency and electrical performance. We determined that the Al_0.30Ga_0.70N cap layer should be around 2 nm and the growth temperature of the GaN barrier should be approximately 75° C higher than the growth temperature of the InGaN QW to maximize the LED efficiency, minimize the forward voltage, and maintain good morphology. Optimized Al_0.30Ga_0.70N cap growth conditions within the active region resulted in high efficiency green LEDs with a peak external quantum efficiency (EQE) of 40.7% at 3 A/cm². At a normal operating condition of 20 A/cm², output power, EQE, forward voltage, and emission wavelength were 13.8 mW, 29.5%, 3.5 V, and 529.3 nm, respectively.