Hourglass-graded heterostructures as a possible route towards extremely efficient light emitting diodes

In this study a theoretical analysis of hourglass-graded light emitting diodes (LEDs) is provided. The term hourglass-grading refers to the placement of a wide band gap material at the diode contacts, smoothly tapering to a smaller band gap material in the active centre region. Utilizing AlGaN as our model system, we show that such a device can both effectively confine carrier recombination and mitigate overflow under high doping conditions. Moreover, by lowering the Auger coefficient of recombination in the active region, room temperature internal quantum efficiencies of 95% or more might be achieved in hourglass-graded LEDs at drive currents near 10³ A cm⁻². (paper)