Tandem Structure for Efficiency Improvement in GaN Based Light-Emitting Diodes

The improvement in efficiency of nitride-based light-emitting diodes by the implementation of a vertically stacked tandem structure is investigated. The electrical and optical characteristics of an LED with a tunnel junction inserted between two active regions are modeled, and the wall-plug efficiency gain of the tandem LED is shown to start at 4.2% at low output powers (27.6 mW), with increasing efficiency gains with increased output power due to the alleviation of efficiency droop. The TLED concept further enables optimization of device structure, allowing removal of electron blocking layer, and optimization of number of quantum wells for improvement in efficiency.