PECVD grown SiN photonic crystal micro-domes for the light extraction enhancement of GaN LEDs

In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the sapphire substrate is reflected upwards to the top surface and the amount of light extracted from the LED is expected to increase. In an alternative approach, SiN micro-domes forming a two dimensional photonic crystal, 2 μm in diameter and 80 nm in height in average, are deposited on the light emitting surface of the device with a period of 2 μm. Coating the backside with Ag has increased the efficiency of a top emitting LED by 11%. By introducing the SiN photonic crystal onto the Ag backside coated sample, total internal reflection is reduced via scattering and the amount of light emitted has been increased by 30% at 5·104 mA/cm2. Integration of SiN micro-domes with Ag coating has significantly impacted light extraction which has been shown to increase the efficiency of GaN based LEDs. Fabrication process and the results are discussed in detail

Distributed contact flip chip InGaN/GaN blue LED; comparison with conventional LEDs

This paper presents high performance, GaN/InGaN-based light emitting diodes (LEDs) in three different device configurations, namely Top Emitting (TE) LED, conventional Flip Chip (FC) and Distributed Contact (DC) FC. Series resistances as low as 1.1 Omega have been obtained from FC device configurations with a back reflecting ohmic contact of Ni/Au/RTA/Ni/Ag metal stack. A small shift has been observed between electroluminescence (EL) emissions of TE LED and the FC LEDs. In addition, FWHM value of the EL emission of DCFC LED has shown the minimum value of 160 meV (26.9 nm). Furthermore, DCFC LED configuration has shown the highest quantum efficiency and power output, with 330 mW at 500 mA current injection, compared to that of traditional wire bonded TE LEDs and the conventional FC LEDs

The Pyrimidine Operon pyrRPB-carA from Lactococcus lactis

The four genes pyrR, pyrP, pyrB, and carA were found to constitute an operon in Lactococcus lactis subsp. lactis MG1363. The functions of the different genes were established by mutational analysis. The first gene in the operon is the pyrimidine regulatory gene, pyrR, which is responsible for the regulation of the expression of the pyrimidine biosynthetic genes leading to UMP formation. The second gene encodes a membrane-bound high-affinity uracil permease, required for utilization of exogenous uracil. The last two genes in the operon, pyrB and carA, encode pyrimidine biosynthetic enzymes; aspartate transcarbamoylase (pyrB) is the second enzyme in the pathway, whereas carbamoyl-phosphate synthetase subunit A (carA) is the small subunit of a heterodimeric enzyme, catalyzing the formation of carbamoyl phosphate. The carA gene product is shown to be required for both pyrimidine and arginine biosynthesis. The expression of the pyrimidine biosynthetic genes including the pyrRPB-carA operon is subject to control at the transcriptional level, most probably by an attenuator mechanism in which PyrR acts as the regulatory protein