No abstract

Indium gallium nitride (InGaN)-based light-emitting diodes (LEDs) are considered a promising candidate for red-green-blue (RGB) micro displays. Currently, the blue and green LEDs are efficient, while the red ones are inefficient for such applications. This paper reports our work of creating efficient InGaN-based orange and red LEDs on silicon(111) substrates at low current density. Based on the structure of InGaN yellow LEDs, by simply reducing the growth temperature of all the yellow quantum wells (QWs), we obtained 599 nm orange LEDs with peak wall-plug efficiency (WPE) of 18.1% at 2    A / cm 2 . An optimized QW structure was proposed that changed two of the nine yellow QWs to orange ones. Compared with the sample containing nine orange QWs, the sample with two orange QWs and seven yellow QWs showed similar emission spectra but a much higher peak WPE up to 24.0% at 0.8    A / cm 2 with a wavelength of 608 nm. The improvement of peak WPE can be attributed to the improved QW quality and the reduced active recombination volume. Subsequently, a series of efficient InGaN-based orange and red LEDs was demonstrated. With further development, the InGaN-based red LEDs are believed to be attainable and can be used in micro LED displays.

No abstract

No abstract

The potential of multicolor semiconductor electroluminescence in solid-state lighting has been extensively pursued due to the energy-saving and smart-lighting as compared to conventional phosphor-converted white light sources. Here, we demonstrate a highly efficient 525 nm GaN-based green light-emitting diode (LED) with a sandwich-like multiple quantum well (MQW) structure grown on patterned Si(111) substrates. Performance enhancement can be achieved by adjusting the thicknesses of the three quantum barriers close to p-GaN in the interior of the sandwich MQW. Samples A, B, and C, with an optimized barrier thickness of 13, 10, and 8 nm, showed peak external quantum efficiency (EQE) values of 55.6%, 56.2%, and 49.0%, respectively. Under normal working conditions (350 mA, current density 35 A/cm2), the output power, EQE, forward voltage, and dominant wavelength of the sample representing the best performance were 306.0 mW, 37.0%, 2.76 V, and 525 nm, respectively. This work might provide an economically feasible way to realize volume-produce of highly efficient InGaN green LEDs on silicon substrates.

TiO 2 photocatalysts doped with alkaline-earth metal ions were prepared by the impregnation and coprecipitation methods. The sample were characterized by XRD, XPS and IR spectroscopy. Their activities were evaluated by the photocatalytic production of hydrogen. The activities of the doped photocatalysts dopended on the size of the dopant ions and the doping method. The optimum molar contents of dopant ions Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ were 1.25, 1.25, 2.25, 2.25 and 2.25 at. %, respectively. The optimum calcination temperature and time were 400°C and 1 h.

No abstract

The authors report the enhancement of the bandgap emission from ZnO thin films by surface modification and surface plasmon cross-coupling. 12-fold and twofold enhancements of bandgap emission from the metal side of ZnO film were observed by sputtering Pt nanopattern and Pt film onto ZnO film, respectively. Time-resolved photoluminescence indicates that the decay time is slowed down by Pt capping, contrary to common observations. The "abnormal" phenomena are interpreted by considering both the surface modification and surface plasmon coupling.