White-light emission from InGaN/GaN quantum well microrings grown by selective area epitaxy

Monolithic white-light-emitting diodes(white LEDs) without phosphors are demonstrated using In GaN/GaN multiple quantum wells(MQWs) grown on GaN microrings formed by selective area epitaxy on SiO_2 mask patterns. The microring structure is composed of {1-101} semi-polar facets and a(0001) c-plane, attributed to favorable surface polarity and surface energy. The white light is realized by combining short and long wavelengths of electroluminescence emissions from In GaN /GaN MQWs on the {1-101} semi-polar facets and the(0001) c-plane,respectively. The change in the emission wavelengths from each microfacet is due to the In composition variations of the MQWs. These results suggest that white emission can possibly be obtained without using phosphors by combining emission light from microstructures.

Site-controlled formation of InGaAs quantum nanostructures——Tailoring the dimensionality and the quantum confinement

We report on InGaAs quantum disks （QDks） controllably formed on the top （001） facet of nano-patterned GaAs pyramidal platforms. The QDks exhibit pyramidal shape with special facets and varied dimensions, depending on the GaAs pyramidal buffer and the amount of InGaAs deposited. The formation of QDks is explained by the overgrowth of an InGaAs layer and thereafter coalescence of small InGaAs islands. Photoluminescence （PL） characteristics of ensemble QDks and exciton features of individual QDks together demonstrate that we may achieve a transition from zero-dimensional （0D） to two-dimensional （2D） quantum structure with increasing QDk size. This transition provides the flexibility to continuously tailor the dimensionality and subsequently the quantum confinement of semiconductor nanostructures via site-controlled self-assembled epitaxy for device applications based on single quantum structures.