Long Wavelength Nanowire Light Emitting Diodes

Green (lambda similar to 540 nm) - and red-emitting (lambda similar to 610 nm) InGaN/GaN disks-in-nanowires have been grown by RF plasma-assisted molecular beam epitaxy on (001) Silicon substrates. The growth of disks-in-nanowires heterostructures has been optimized and the nanowires have been passivated to achieve radiative efficiencies of 54% and 52% in the green and red InGaN disks, respectively. Radiative efficiency increases significantly (by similar to 10%) when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. Light emitting diodes on silicon, incorporating InGaN/GaN quantum disks as the active medium have been fabricated and the devices have been characterized. Quantum Confined Stark Effect (QCSE) blue-shift of 7nm and 15nm have been observed in the measured electroluminescence peak of the green and red LEDs respectively, from which polarization fields have been calculated in the disks to be 605kV/cm for green and 1.26MV/cm for red. For green and red LEDs, external quantum efficiency peaks at current densities of similar to 25A/cm(2) and 12A/cm(2), respectively. To improve light extraction efficiency, LED heterostructures have been transferred to Ag mirrors from the silicon growth substrate and preliminary device results have been demonstrated.