Perforated GaN-based light-emitting diodes (LEDs) with an array of plasma-etched microholes penetrating through the
active region were fabricated using lithography and plasma etching. Plasma damage on the microhole sidewalls led to an
increase in junction leakage by up to seven orders of magnitude and a reduced light emission in the low injection regime.
It was found that KOH can etch off the plasma-damaged materials, leading to a complete suppression of surface leakage
currents. It however attacked metal contacts and increased the forward turn-on voltage. Thermal annealing removed
damage in the near-surface bulk region, whereas (NH4)2S treatment only passivated the defect states at the immediate
surfaces. Both methods produced a partial restoration of the forward-bias characteristics. It has been demonstrated that
annealing at 700 °C used in conjunction with prolonged sulfide passivation can remove or passivate all plasma-induced
defects and result in a complete suppression of surface leakage in the perforated LEDs. This work is an important step
toward developing high-efficiency photonic crystal-integrated LEDs, in which light can only be coupled to radiation
modes but the undesirable guided light emission is inhibited.
InGaN-based LEDs suffer from a significant drop in quantum efficiency (QE) under high-current operation. We studied
the Electroluminescence (EL) of InGaN-based multiple-quantum-well green LEDs on both Sapphire and free standing
Bulk GaN, in an attempt to shed light on the underlying mechanism for the efficiency droop problem. The density of
microstructural defects in the LED on GaN was substantially reduced, leading to a significant reduction in defectassisted
tunneling currents and an improved injection efficiency under low bias. The LED on GaN outperformed the
LED on sapphire at low injection currents and exhibited a ~65% peak internal quantum efficiency. However, it suffered
from even more dramatic efficiency roll-off which occurs at a current density as low as 0.3 A/cm2. The EQE roll-off is
mitigated when the LEDs were tested at elevated temperatures. These results are explained as the combined result of
efficient current injection and significant carrier overflow in a high-quality LED.