| Nitride-based light emitting diodes (LEDs) and lasers are in high demand due to their numerous applications including those 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 (QW) based devices suffer from large efficiency droop and peak emission shift at high injections, large threshold current densities in lasers, and there is difficulty in achieving long wavelength green- and red-emitting devices. In this dissertation, quantum dot (QD) based devices with superior optical properties have been demonstrated.;Self-assembled InGaN/GaN QDs were grown and optimized in a plasma-assisted molecular beam epitaxy (PA-MBE) system via strain relaxation and were extensively characterized to demonstrate dots with smaller polarization field and larger electron-hole wavefunction overlap, resulting in higher radiative efficiencies and no S-shaped peak emission shift with temperature which is typically associated with In clustering effects. Blue- and green-emitting QD LEDs with reduced efficiency droop and peak emission shift were demonstrated. Small signal modulation of QW and QD based high speed LEDs was done to understand the recombination dynamics of carriers in the active region. Additionally, a study on the use of these QDs as a dislocation filter was also investigated with the objective of growing devices with lower defect densities.;Growth conditions for the laser cladding (AlGaN) and waveguide (InGaN) layers grown by PA-MBE were optimized to obtain epitaxial layers of high crystalline quality which were used to demonstrate some of the first nitride QD lasers. Ridge waveguide blue-emitting (wavelength=418 nm and 478 nm) QD lasers were grown and characterized with significantly lower threshold current densities, small peak emission shift with injection and high differential gain. The first nitride-based red lasers were also demonstrated incorporating In0.4Ga 0.6N/GaN QDs as the active region having low threshold current density and peak emission shift.;Additionally, the optical and spin properties of carriers in InGaN-dot-in-GaN nanowires having similar dimensions to the self-assembled QDs were explored. The nanowires have a high aspect ratio and filter the dislocations through their sidewalls, resulting in high radiative efficiencies. A long spin relaxation time (120 ps) for the nitride material was reported. |
