Shigefusa F. Chichibu

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Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in(More)
Impacts of structural and point defects on the carrier (exciton) recombination dynamics in wide bandgap semiconductors such as AlN, high AlN mole fraction AlxGa1-xN alloys, and GaN were studied in this project. For this purpose, we quantified the radiative lifetimes (R) and nonradiative lifetimes (NR) for the near-band-edge (NBE) emission by measuring the(More)
The local structure around In atoms in an m-plane In0.06Ga0.94N film coherently grown on a freestanding m-plane GaN substrate was investigated by polarization-dependent X-ray absorption fine-structure. A step-by-step fitting procedure was proposed for the m-plane wurtzite structure. The interatomic distance for the first nearest neighbour In-N atomic pairs(More)
Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Γ(1) and Γ(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k is perpendicular to a and E is parallel to c configurations for an(More)
Planar vacuum-fluorescent-display devices emitting polarized UV-C, blue, and green light are demonstrated using immiscible Al1-x Inx N nanostructures grown in nonpolar m-directions. Despite the presence of high concentration of nonradiative recombination centers, the Al1-x Inx N nanostructures emit polarized light with the luminescence lifetimes of 22-32 ps(More)
Concept, equipment, and exploitation of spatio-time-resolved cathodoluminescence (STRCL) spectroscopy will be presented. As one of its advantages is unlimited bandgap energy of the sample, we show STRCL data of high AlN mole fraction Al<sub>x</sub>Ga<sub>1-x</sub>N structures. For understanding the mechanisms of the improvement in the luminescence(More)
In order to understand the reason why doping with Si in the &#x201C;wells&#x201D; enhanced the NBE emission efficiency, STRCL measurements and 1D-SCSP calculations were carried out on the Al<sub>0.68</sub>Ga<sub>0.32</sub>N / Al<sub>0.77</sub>Ga<sub>0.23</sub>N MQWs with different Si-doped layers. The increase in &#x03C4;NR, i.e decrease in the(More)
Acidic ammonothermal method is one of the most promising techniques which enable the mass production of large diameter bulk GaN crystal. State-of-the-art high-power light-emitting diodes and laser diodes are usually fabricated on GaN substrates grown by hydride vapor phase epitaxy. However, to realize vertically conducting high-power GaN switching devices,(More)
Light polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1-xN epilayers suffering from anisotropic stresses are quantitatively explained. The epilayers were grown on an m-plane freestanding GaN substrate by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods. The light polarization(More)
Optical gain characteristics have been theoretically calculated in AlGaN and InGaN quantum-well structures considering the effects of alloy compositional fluctuation in the active layers. It is found that the difference in optical gain characteristics between AlGaN and InGaN lasers becomes small with increasing the degree of alloy compositional fluctuation.