Size-dependent efficiency and efficiency droop of blue InGaN micro-light emitting diodes

The mechanisms of size-dependent efficiency and efficiency droop of blue InGaN micro-pixel light emitting diodes (mu LEDs) have been investigated experimentally and by simulation. Electrical characterisation confirms the improvement of current spreading for smaller mu LEDs, which enables the achievement of the higher efficiency at high injection current densities. Owing to the higher ratio of sidewall perimeter to mesa area of smaller mu LEDs, a lower efficiency was observed at a low injection current density, resulting from defect-related Shockley-Read-Hall non-radiative recombination. We demonstrate that such sidewall etch defects can be partially recovered by increased thermal annealing time, consequently improving the efficiency at low current densities. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769835]