Micro-scaling of indium gallium nitride blue and green light-emitting diodes
University of California Santa Barbara (UCSB) in the USA and Seoul Viosys in South Korea have been exploring the effects of scaling down the diameters of green and blue indium gallium nitride (InGaN) micro light-emitting diodes (LEDs) [Jordan M. Smith et al, Appl. Phys. Lett., vol116, p071102, 2020]. Often external quantum efficiency (EQE) in LEDs is reduced as dimensions scale down due to non-radiative recombination at device surfaces.
The UCSB/Viosys team found a marked such effect for the blue devices, but the green LEDs were less affected. Indeed, at LED diameters less than 10μm, the green devices became more efficient than the blue ones.
The researchers also suggest that there may be a similar diameter crossover effect for red InGaN LEDs in comparison with the standard commercial aluminium gallium indium phosphide (AlGaInP) products. One would expect red InGaN LEDs to suffer even higher carrier localization effects, further reducing the surface recombination velocity (SRV).