III-Nitride Self-Assembled Quantum Dot Light Emitting Diodes and Lasers
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Nitride-based light emitting diodes (LEDs) and lasers are in high demand due to their numerous applications including in solid state lighting, optical data storage, mobile projectors, heads-up displays, and other military and medical applications. Current state-of-the-art quantum well based devices suffer from large efficiency droop and peak emission shift at high injections, large threshold current densities in lasers, and difficulty in achieving long wavelength green- and red-emitting devices. As an alternative, InGaN/GaN self-assembled quantum dot (QD) based devices with superior optical properties were demonstrated. The QDs were optimized to have reduced dislocation density, smaller polarization field, and larger electron-hole wavefunction overlap, resulting in higher radiative efficiencies. Blue- and green-emitting QD LEDs with reduced efficiency droop and peak emission shift were demonstrated. Ridge waveguide blue-emitting (Î»=418 nm) QD lasers were demonstrated with significantly lower threshold current densities ~930 A/cm2, a small peak emission shift of 4.8 nm and a high differential gain. The first ever nitride-based red lasers were also demonstrated incorporating In0.4Ga0.6N/GaN QDs as the active region characterized by a low threshold current density of ~2.5 kA/cm2 and a peak emission shift of only 11.6 nm.