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.

High crystalline quality of SiGe fin fabrication with Si-rich composition area using replacement fin processing

A high crystalline quality of SiGe fin with an Si-rich composition area using the replacement fin processing is systematically demonstrated in this paper.The fin replacement process based on a standard FinFET process is developed.A width of less than 20-nm SiGe fin without obvious defect impact both in the direction across the fin and in the direction along the fin is verified by using the high angle annular dark field scanning transmission electron microscopy and the scanning moiréfringe imaging technique.Moreover,the SiGe composition is inhomogenous in the width of the fin.This is induced by the formation of 111 facets.Due to the atomic density of the 111 facets being higher,the epitaxial growth in the direction perpendicular to these facets is slower than in the direction perpendicular to 001.The Ge incorporation is then higher on the 111 facets than on the 001 facets.So,an Si-rich area is observed in the central area and on the bottom of SiGe fin.

Semi-polar GaN LEDs on Si substrate

Growth of semi-polar （1-101）GaN has been attempted on a patterned （001） silicon substrate adopting selective area MOVPE. The growth was initiated on （111） facets of the Si, which had been prepared by anisotropy etching in a KOH solution. A uni- form semi-polar layer was achieved by coalescence of stripes. Since the growth was performed on facets, the surface was atomically fiat in AFM surface analyses. By using a high temperature grown A1N nucleation layer, we achieved low threading dislocation density at the top most surface. Moreover, by tilting the c-axis of the GaN on the Si substrate, the effect of the thermal expansion coefficient mismatch was much reduced. As the result, we achieved a crack free （1-101）GaN template on （001）Si. On the thus prepared （1-101）GaN, a GalnN/GaN LED was fabricated, which showed excellent performance with weak quantum confined Stark effect.

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.