-
[show abstract]
[hide abstract]
ABSTRACT: In this study, a GaN-based light-emitting diode (LED) with a distributed Bragg reflector (DBR) current blocking layer (CBL) beneath the p-pad electrode is demonstrated. A high reflectivity DBR structure is composed of five periods SiO<sub>2</sub> and TiO<sub>2</sub> layers. At a driving current of 20 mA, the light output power of the LEDs with DBR CBL was 16.8% and 11.3% higher than the LEDs without and with SiO<sub>2</sub> CBL. The improvement is contributed to the DBR CBL can deflect the current away from the p-electrode pad and also prevent the light absorption by the opaque metal electrode. It was found that LEDs with DBR CBL shows better current spreading and broader far-field pattern.
IEEE Photonics Technology Letters 08/2011; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We describe a method to enhance the light output power of nitride-based light-emitting diodes (LEDs) through the coupling of multiple quantum wells (MQWs) with localized surface plasmon (LSP). The LSP was generated on an Ag nanotriangle array (NTA) on a 40-nm-thick p-type GaN layer beneath the p-pad of the LED, which was partially etched by inductively coupled plasma system. The Ag NTA was fabricated by nanosphere lithography. The resonant frequency of a generated LSP can be precisely controlled by changing the size of the polystyrene nanosphere and the Ag deposition thickness. Under the optimum conditions, the light output power of LED with an Ag NTA was 15.4% higher than LED without an Ag NTA at an inject current of 20 mA. The improvement in light output power can be attributed to the coupling effect between MQW and LSP.
IEEE Photonics Technology Letters 08/2010; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of period of electron emitter multiple-quantum well (EE-MQW) structure on the structural, electrical, and optical characteristics of nitride-based light-emitting diodes (LEDs) were investigated. From the lattice constant results of InGaN/GaN multiple-quantum well (MQW) by the high resolution X-ray diffraction, the compressive strain of InGaN/GaN MQW could be released gradually when the period of EE-MQW structure increases. Therefore, the leakage current reduces and the ESD endurance ability enhances with increasing period of EE-MQW structure. On the other hand, the electron injection efficiency will also be improved by inserting EE-MQW structure. When the period of EE-MQW structure increases, the forward voltage and series resistance both decrease. Due to the improved electron injection efficiency and crystalline quality, the luminance intensity increases with increasing period of EE-MQW structure. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 04/2010; 7(7‐8):2162 - 2164.
-
[show abstract]
[hide abstract]
ABSTRACT: GaN-based light-emitting diodes (LEDs) with an emitting wavelength of 450 nm were grown on nano-patterned sapphire substrates (NPSS) fabricated by nanosphere lithography. The crystalline quality of the epitaxial film could be improved by using the NPSS technique. The output power of LED grown on NPSS was 1.3 and 1.11 times higher than those of LEDs grown on conventional and patterned sapphire substrates at the injection current of 20 mA, respectively. The enhancement in output power could be contributed to the efficiently scattering by NPSS. But some voids formed at the GaN/NPSS interface cause a thermal dissipation problem of NPSS LED operated at high injection current.
IEEE Photonics Technology Letters 08/2008; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: GaN-based light-emitting diodes (LEDs) with nanosphere layers were fabricated by spin-coating method. It was found that the LEDs with and without nanosphere layers had the same electrical characteristics. With 20 mA current injection, the luminance intensities of the LEDs with nanosphere layers of 300 nm and 500 nm diameters exceeded that of the LED without nanosphere layers by 5.72% and 9.05%, respectively. The improvement of the luminance intensity is attributed to the periodic structure of nanosphere layers increasing the light extraction of photons.
Nanoelectronics Conference, 2008. INEC 2008. 2nd IEEE International; 04/2008
-
[show abstract]
[hide abstract]
ABSTRACT: To maximise device utilisation, a heterogeneous field programmable gate array (FPGA) provides either an array of homogeneous lookup tables (LUTs) of different sizes or an array of physically heterogeneous LUTs. It is shown that heterogeneous FPGAs have a significant number of desirable attributes. A technology mapping algorithm is proposed for heterogeneous FPGAs. The technology mapping problem is first formulated as a flow network problem. Then, an algorithm based on the min-cost max-flow algorithm is presented to select a proper set of feasible LUTs for various objectives. Two objectives: (i) the minimum number of LUTs; and (ii) the total area composed of LUTs and routing area are discussed. The algorithm is tested on the MCNC benchmark circuits and produces better characteristics than existing LUT based FPGA mapping algorithms.
IEE Proceedings - Computers and Digital Techniques 12/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents a recent study of avionics system design and implementation for small aircraft. Avionics system is one of the most important systems to all kinds of aircraft. For digital avionics system integration, a hybrid data bus is proposed in this development. The proposed hybrid data bus (HDB) adopts some characteristics from time trigger protocol (TTP) in conjunction with the controller area node (CAN) to simplify the data bus structure and enhance system reliability in the applications. The proposed hybrid data bus system is designed and fabricated for test as a preliminary solution. In addition to data bus system, a virtual flight instrument with geographic information system (GIS) is integrated into cockpit display together with mobile communication surveillance for low altitude flight. The overall system integration brings in new era of digital avionics for small aircrafts.
Digital Avionics Systems Conference, 2005. DASC 2005. The 24th;
