Ultimate limit and temperature dependency of light-emitting diode efficiency

We discuss the ultimate limit of performance of semiconductor light-emitting diodes (LEDs) and its dependence on temperature. It is known that in high quality semiconductor materials it is, in principle, possible to reach wall plug efficiencies exceeding unity, which allows electroluminescent cooling in addition of very high efficiency light emission. Our simulation results suggest a few fairly simple measures that may further improve the external quantum efficiency (EQE) of LEDs toward the electroluminescent cooling limit. These include reducing the current density, modifying the LED structure by making thicker active regions and barrier layers, and doping of the active material. Our calculations also indicate that, contrary to the present understanding, operating LEDs at relatively high temperatures of 400-600 K may, in fact, improve the performance. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3125514]