From Ultraviolet to Green InGaN-Based Conventional and Resonant-Cavity Light-Emitting Diodes Grown by Molecular Beam Epitaxy

Abstract

InGaN/GaN multiple quantum wells grown by molecular beam epitaxy were used as the active layer of standard and resonant-cavity light emitting diodes. Varying the In content in the wells from 1% to 35% and the well thickness from 1 to 2.5 nm, the room temperature electroluminescence can be tuned from 370 nm (ultraviolet) to 510 nm (green). The main factor that determines the emission energy in the well is the exciton localization for narrow wells, whereas for well thicknesses larger than 3 nm the piezoelectric field is the key factor, even for high In contents. Green resonant-cavity light emitting diodes have been successfully fabricated with a semitransparent AlGaN/GaN-based distributed bragg reflector as bottom mirror and an Al coating as top mirror. The external efficiency of those devices is increased by a factor of 10 compared to standard light emitting diodes.