No abstract

Photosensitive sol-gel hybrid (SGH) materials exhibited the peculiar photoinduced migration behavior of unreacted molecules from unexposed areas to exposed areas by selective UV exposure. Using the photoinduced migration mechanism of the photosensitive SGH materials, the microlens array (MLA) with a smooth surface was directly photofabricated, and the focal length was controlled by changing the photoinduced migration parameters. The higher photoactive monomer content and the thicker film creating a higher curvature produced a smaller focal length of the MLA. Thus, a simple fabrication and easy control of the focal length can be applicable to a fabrication of an efficient MLA.

No abstract

We observed the green MQWs grown on FS-GaN substrates leading to less generation of dislocation, V-defect, and stacking fault than those on sapphire by AFM and TEM. The temperature-dependent PL spectral peak energies of the green MQWs grown on FS-GaN substrates reveal more clear "S"-shaped behaviors due to stronger carrier localization than those on sapphire substrates. Also, the green MQWs grown on FS-GaN have the higher internal quantum efficiency (IQE) of 9 ~ 12% in compared to those grown on sapphire at the same MQW thickness and wavelength of 530 ~ 540 nm. These results will be due to the effects of the enhanced carrier localization and the reduced quantum confined stark effect (QCSE) by reason of the optical-loss reduction as decreasing the defect density and the piezoelectric field reduction as decreasing the relaxation of strain. We could identify that the green MQWs grown on FS-GaN substrates have the superior characteristics of the optics, structure, and surface to those on sapphire substrates. 1 Introduction GaN-based Light-emitting diodes(LEDs) have attracted great attention in research and industry [1,2]. Blue and green LEDs have been extensively used as highly efficient light sources for traffic light lamps, mobile and full-color display applications [3,4]. In particular, white LED have recently issued by being applied optical source of backlighting unit in liquid-crystal display (LCD), automotive and outdoor lighting [5][6][7][8][9]. However, the property such as the optical efficiency is not yet sufficient to satisfy consumer demands. Commercially, The GaN-based LEDs grown on sapphire and SiC substrate have the high density of threading dislocations, and other structural defects such as stacking faults, inversion domains etc., because of the large difference in the lattice constant and thermal expansion coefficient between GaN film and sapphire substrate, or the increase of In content in the active region. Particularly, as the wavelength is increased from 460 nm in the blue to 545 nm in the deep green by the increase of In content, indicates the rapid deterioration in emission efficiency [10][11][12][13][14][15][16]. Recently the internal quantum efficiency (IQE) for Ga x In 1-x N-based green MQW grown on sapphire substrate has been reported about 8% at λ peak = 540 nm [17]. In this paper, we compare the surface, structural, and optical characteristics of green InGaN/GaN multiple-quantum-well (MQW) grown on FS-GaN and sapphire substrates. The comparative study on MQW with various wavelength regions shows the IQE differences in relation to the effect of defect reduction and the decreased strain relaxation.