Light Extraction and Auger Recombination in AlGaN-Based Ultraviolet Light-Emitting Diodes

AlGaN-based 300-nm ultraviolet (UV) light-emitting diodes (LEDs) with various p-n junction mesa perimeter-to-area (P/A) ratios and mesa depths were fabricated. As the mesa P/A ratio increases from
$0.0133\,\,\mu \text{m}^{-1}$
to 0.157
$\mu \text{m}^{-1}$
and the mesa depth increases from 550 nm to 1700 nm, the peak external quantum efficiency (EQE) increases from 2.93% to 4.89%. Fitting results from the ABC+f(n) model reveal that the light-extraction efficiency (LEE) is the major factor limiting the EQE, which can be enhanced by increasing the mesa P/A ratio and mesa depth. On the other hand, increasing the mesa P/A ratio and mesa depth also leads to increased Auger recombination coefficient from
$1.11\times 10^{-31}$
cm
$^{6}\text{s}^{-1}$
to
$2.11\times 10^{-30}$
cm
$^{6}\text{s}^{-1}$
, and the probable mechanism is defect-assisted Auger recombination at mesa sidewall by etching damage. In spite of the decreased internal quantum efficiency by Auger recombination, the improved LEE by increasing the mesa P/A ratio and mesa depth is still the major factor for the EQE at the current density below 150 A/cm
²
for UV LEDs.