The efficiency challenge of nitride light‐emitting diodes for lighting (Phys. Status Solidi A 5∕2015). Issue 5 (May 2015) - Weisbuch, Claude
Abstract The award of the 2014 Nobel Prize in Physics to I. Akasaki, H. Amano and S. Nakamura "for the invention of efficient blue light‐emitting diodes" (LEDs) illustrates the worldwide societal impact of nitrides. However, despite the remarkable achievements of the pioneers and their followers, there are still scientific and technological roadblocks for LEDs to reach their physical limits. Claude Weisbuch and coworkers (see pp. 899–913) discuss the challenges encountered by LEDs in their generalized application to solid‐state lighting. Today's high performance is only obtained in the blue/violet spectral range and at low carrier injection, a few A/cm2. Operation at high current densities, a prerequisite to lower lamp costs, leads to a nonlinear phenomenon, called droop, which diminishes the internal quantum efficiency (IQE) as a function of current density. This results in two major components of the cost of ownership of LED lamps: (i) one needs multiple LED chips to deliver the needed light output, raising the initial lamp cost; (ii) LEDs are operated at a diminished IQE which increases the electricity costs, and also increases the thermal load putting a costly burden on the package. The main challenge for LEDs is then to reduce the droop phenomenon, which will result in high‐output single chip lamps, higher efficiencies and lower‐cost lamp packages. [To honour the laureates of the Nobel Prize in Physics 2014, the cover of this pss (a) issue shows a specially designed pss logo assembled from blue nitride LEDs (courtesy of Armin Dadgar, Technical University of Magdeburg)].