Abstract
We investigated the effects of different well shapes on the external quantum efficiency (EQE) and the efficiency droop in wide-well InGaN/GaN double-heterostructure light-emitting diodes. For forward current densities in the measurement range of greater than 135 A/cm2, the device featuring a trapezoidal well exhibited improved EQEs and alleviative efficiency droop, relative to those of the device featuring a rectangular well. The decreased Auger loss has been proposed as the main reason for the greater maximum efficiency that occurred at high current density (>50 A/cm2). For the devices incorporating trapezoidal and rectangular wells, the EQEs at 200 A/cm2decreased by 14 and 40%, respectively, from their maximum values, resulting in the EQE at a current density of 200 A/cm2of the device featuring a trapezoidal well being 17.5% greater than that featuring a rectangular well. These results suggest that, in addition to the decreased Auger loss, the alleviation in efficiency droop at higher current densities might be due to higher internal quantum efficiency resulted from the improved carrier injection efficiency of the trapezoidal well.
Highlights
Research and development related to InGaN-based lightemitting diodes (LEDs) is currently of very high interest because of their applications as replacements for conventional lighting devices, including incandescent light bulbs, fluorescent lamps, and automotive head lamps
This result violates the notion that using the trapezoidal well would induce a higher barrier to carrier flow than that obtained with a rectangular well; it is inconsistent with previous reports of an InGaN/GaN multiple quantum wells (MQWs) LED [17] and the use of an AlInGaN barrier to minimize the polarization mismatch [7]
We have investigated efficiency droop phenomena in widewell InGaN-based DH LEDs featuring trapezoidal and rectangular active regions
Summary
Research and development related to InGaN-based lightemitting diodes (LEDs) is currently of very high interest because of their applications as replacements for conventional lighting devices, including incandescent light bulbs, fluorescent lamps, and automotive head lamps. Experimental and theoretical studies have suggested several different mechanisms to explain the phenomenon of efficiency droop, including carrier delocalization from In-rich clusters [1], junction heat [2], decreased injection efficiency [3], Auger loss [4, 5], polarization mismatches [6, 7], current rollover [8,9,10], defect-related tunneling [11], and interface states [12]. Most studies on the efficiency droops of LEDs have been made using InGaN/GaN MQWs as the active region; only a few examinations have been made into the International Journal of Photoenergy mechanisms in InGaN-based DH structures. We investigated the impacts of trapezoidal and conventional rectangular wells on the efficiency droop phenomena when using a wide-well InGaN/GaN DH structure as the active region
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