A simple fluorescent probe based on an ortho-hydroxy aldehyde-functionalized coumarin showed selective responses to homocysteine and cysteine by fluorescence turn-on.

GaN-based light-emitting diodes (LEDs) were fabricated on a micro-lens patterned sapphire substrate (ML-PSS). ML patterning on the sapphire substrate was carried out by using photolithography with photo-resist reflow technique and dry etching process using chlorine based inductively coupled plasma. The ML-PSS was prepared using a periodic ML pattern with diameters of 3 µm and spacing of 2, 4, and 5 µm, respectively, on the c-plane sapphire substrate. The leakage current of the LEDs fabricated on the ML-PSS greatly decreased compared to that of a conventional LED and it decreases with increasing ML-pattern spacing; it decreases from 1.8 to 0.2 µA at reverse voltage of 15 V as the ML-pattern spacing is increased from 2 to 5 µm. The output power of the LED with 5 µm spacing was about 155% higher than that of a conventional LED and about 10% higher than that of the LED on the PSS with spacing of 2 µm. This improvement of the output power is contributed not only by reduction of dislocation density depending on spacing of patterning but also by the enhancement of light extraction efficiency with outcoupling via the ML patterned facets on sapphire substrate.

. Gy, 68.55.Jk, 71.20.Br, 78.30.Fs, 78.55.Cr In x Ga 1-x N films and In x Ga 1-x N/GaN multiple quantum wells (MQWs) were grown on highly tensile strained GaN/Si(111) structure by MOCVD. Due to the large difference of lattice constant and thermal expansion coefficient between GaN and Si, GaN growth on Si(111) substrate usually leads to an initially high dislocation density and cracks. We demonstrate the low dislocation density and crack-free GaN films grown on Si(111) substrate introducing an AlN/GaN strain compensation layer and Si x N y dislocation masking layer. The Raman shift of E 2 phonon peak of GaN films on Si(111) substrate indicate the strong tensile stress (0.474 GPa). The In x Ga 1-x N bandgap energy depended on In-composition, which can be fitted by a larger bowing parameter of b = 4.5 eV in Ga-rich region (x < 0.25). Also, crack-free In x Ga 1-x N/GaN MQWs with blue and green emissions were demonstrated.

For high efficiency GaN-based light-emitting diodes (LEDs), Al 2 O 3 powder coating and surface texturing were investigated using natural lithography and dry-etching methods to improve the light-output power of the GaN-based LED. The 300-nm-size Al 2 O 3 powder is coated on the indium tin oxide (ITO) surface at various conditions using a spin-coating method. The morphologies of the ITO surface were observed using a scanning electron microscope. The Al 2 O 3 powder is left on the ITO surface after surface-texturing to increase extraction efficiency. The light output powers of the surface-textured GaN-based LEDs coated with the Al 2 O 3 powders are enhanced by 66% compared with the conventional LED at 20 mA.

GaN-based light-emitting diodes (LEDs) were fabricated by coating Al 2 O 3 powder on a p-GaN and a semitransparent p-contact metal surface to increase the extraction probability of the internal reflected photons through the Al 2 O 3 powder. The density of the $300-nmdiameter Al 2 O 3 powder was about 1:9 Â 10 13 cm À2 on both surfaces. The forward voltages of the LEDs coated with Al 2 O 3 powder on the p-GaN surface and the semitransparent p-contact metal surface were 4.15 and 3.42 V at 20 mA, respectively. The light output powers of both LED structures with Al 2 O 3 powder coated on the p-GaN and semitransparent p-contact metal surfaces were increased by almost 30% compared with the conventional LED structure without Al 2 O 3 powder coating. #