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

Abstract

The mechanisms of size-dependent efficiency and efficiency droop of blue InGaN micro-pixel light emitting diodes (LEDs) have been investigated experimentally and by simulation. Electrical characterisation confirms the improvement of current spreading for smaller 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 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 densitie

Mesa-height Dependent Quantum Efficiency Characteristics of InGaN Micro-LEDs

“…Micro-LEDs show improved efficiency at high injection current density although the efficiency was affected via side-wall defects induced non-radiative recombination at low injection [4]. The high efficiency at high injection was attributed to enhanced current spreading in micro-LEDs, which resulted in a reduction of efficiency droop effect [5].…”

“…Other potential advantages of micro-LED include enhanced light extraction [6] and suitability in optoelectronic integration [7]. To realize high efficiency micro-LED, the size effect was studied experimentally and by simulation [3,4]. However, further exploration on the design of mesa height (H) is required.…”

“…InGaN-QW-based micro-light-emitting diode (micro-LED) structure was demonstrated to hold unique electrical characteristics suitable for high power LED lighting compared with its large-area counterparts [1][2][3][4]. Micro-LEDs show improved efficiency at high injection current density although the efficiency was affected via side-wall defects induced non-radiative recombination at low injection [4].…”

Planar micro- and nano-patterning of GaN light-emitting diodes: Guidelines and limitations

“…10 The implications of high current density operation are the topic of ongoing research and relate to important challenges of III-nitride research, in particular carrier dynamics 11 and the so-called "efficiency droop." 12,13 Most patterning techniques rely on etching methods. These become increasingly difficult as the pattern size is reduced to a few microns or less and, also, etching damage to the epitaxial structure often deteriorates device performance.…”

InGaN micro-LED-pillar as the building block for high brightness emitters

“…InGaN-QW-based micro-LED structure (µLED-pillar henceforth), used in visible light communication [3] and micro-display [4], were demonstrated to hold unique electrical characteristics suitable for high power LED lighting. It was reported that µLED-pillar with diameter (D) < 100 µm can sustain high injection current density, and showed an improved efficiency at high drive current [5]. A reduced efficiency droop effect can hence be expected in µLED-pillars.…”