High Internal Quantum Efficiency Blue-Green Light-Emitting Diode with Small Efficiency Droop Fabricated on Low Dislocation Density GaN Substrate

We fabricated blue (∼450 nm), blue-green (∼500 nm), and green (∼525 nm) light-emitting diodes (LEDs) of different dislocation densities (DD) and characterized their internal quantum efficiency (IQE). The IQE of the blue LEDs fabricated using GaN substrate exceeded 90% (DD: ∼106cm-2), however, when we used a GaN-on-sapphire substrate (DD: ∼108cm-2), IQE was limited to ∼60%. Droop was reduced by use of the GaN substrate. The junction temperature of the GaN-on-sapphire substrate was found to be ∼200 °C although the junction temperature of the GaN substrate was ∼50 °C when a forward current of 100 A/cm2was driven. A lowering of IQE in green LEDs to ∼60% was observed, even though we used a low-dislocation-density substrate [DD: (1–2)×107cm-2]. The junction temperature of blue-green and green LEDs was about 100 °C when a forward current of 177 A/cm2was driven, which indicated that junction temperature is not a major factor for IQE suppression in green LEDs.