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Zhang M.,Xian Jiaotong University | Yun F.,Xian Jiaotong University | Li Y.,Xian Jiaotong University | Ding W.,Xian Jiaotong University | And 7 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2015

Optimized dual-wavelength InGaN-based vertical light-emitting diode (LEDs) structures were investigated by numerical simulations. The results show that different quantum-well arrangements in the active region play an important role in obtaining dual-wavelength emission. It is a better way to obtain the dual-wavelength with uniform intensity by arranging quantum wells (QW) with low indium content near the p-side and the QW with high indium near the n-side. This is because the QWs with lower indium near the p-side layer have higher hole-injection efficiency. On the other hand, arranging QW with high indium content near the p-side leads to poor hole-injection efficiency due to the high polarization fields. The physical and optical mechanisms of these phenomena were explained by the intensity of electrostatic fields, energy-band diagrams, and carrier-concentration distribution in the active region of LEDs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Huang Y.,Shaanxi University of Technology | Huang Y.,Xian Jiaotong University | Yun F.,Shaanxi University of Technology | Yun F.,Xian Jiaotong University | And 12 more authors.
Applied Physics Express | Year: 2014

We have demonstrated defect-induced color-tunable monolithic GaN-based vertical light-emitting diodes (VLEDs). With Ag nanorod arrays embedded in p-GaN, large numbers of Ga vacancies (VGa) were produced during the thermal bonding process in VLED fabrication. VGa-related donor-acceptor pair (DAP) transitions in p-GaN resulted in red emission in photoluminescence (PL) measurements as well as a broad electroluminescence (EL) emission spectrum extending from green to red. In combination with high-emission-efficiency blue InGaN/GaN multiple quantum wells (MQWs), the emission color of VLEDs can be changed from red to white by increasing the injection current. © 2014 The Japan Society of Applied Physics.

Wang S.,Shaanxi University of Technology | Wang S.,Xian Jiaotong University | Li Y.,Shaanxi University of Technology | Li Y.,Xian Jiaotong University | And 9 more authors.
Optics Express | Year: 2016

We present a facile fabrication process to directly fabricate cone-shaped microwells arrays on single crystal Y3Al5O12:Ce3+ (YAG:Ce) ceramic phosphor platelets (CPPs) by short-pulse laser direct patterning. Compared to unpatterned YAG:Ce CPP with smooth surface, the forward-to-total ratio of emission photons of patterned YAG:Ce CPPs was enhanced from 53.2% up to 78.2%, and the total emission within 4-π degree is 6% higher. The fabricated patterns are also beneficial in increasing the color conversion efficiency of YAG:Ce CPPs by 7.6%. The patterned YAG:Ce CPPs display much better correlated color temperature (CCT) uniformity under varied currents. The angular correlated color temperature uniformity (ACU) of patterned YAG:Ce CPPs reaches as high as 0.933 compared to 0.730 of the unpatterned one. These results suggest that laser patterning of YAG:Ce CPP could effectively manipulate its luminance, chromaticity and illumination pattern, which may lead to further technological advancements for diversified applications of film-type CPPs in highly efficient white LEDs. © 2016 Optical Society of America.

Liu H.,Shaanxi University of Technology | Liu H.,Xian Jiaotong University | Li Y.,Shaanxi University of Technology | Li Y.,Xian Jiaotong University | And 9 more authors.
AIP Advances | Year: 2016

Air-void structure was introduced in GaN-based blue light-emitting diodes (LED) with one-step growth on periodic laser drilling patterned sapphire substrate, which free of any photolithography or wet/dry etching process. The influence of filling factors (FF) of air-void on crystal quality and optical performance were investigate. Transmission electron microscopy images and micro-Raman spectroscopy indicated that the dislocation was bended and the partially compressed strain was released. When FF was 55.43%, compared with the LED structure grown on flat sapphire substrate, the incorporation of air-void was observed to reduce the compressed stress of ∼20% and the luminance intensity has improved by 128%. Together with the simulated reflection intensity enhancement by finite difference time-domain (FDTD) method, we attribute the enhanced optical performance to the combined contribution of strong back-side light reflection of air-void and better GaN epitaxial quality. This approach provides a simple replacement to the conventional air-void embedded LED process. © 2016 Author(s).

Li Q.,Shaanxi University of Technology | Li Q.,Xian Jiaotong University | Gong Z.,Xian Jiaotong University | Li Y.,Shaanxi University of Technology | And 6 more authors.
Nanoscale Research Letters | Year: 2016

Polystyrene sphere was chosen as a catalyst to fabricate indium-tin-oxide (ITO) nanowires (NWs) with a low-temperature (280–300 °C) electron-beam deposition process, bearing high purity. The ITO NWs with diameter of 20–50 nm and length of ~2 um were obtained. X-ray diffraction and high-resolution transmission electron microscope show high crystal quality. The transmittance is above 90 % at a wavelength 400 nm or more, superior to the ITO bulk film. Owing to the unique morphology gradient of the ITO NWs, the effective refractive index of ITO NWs film is naturally graded from the bottom to the top. The ITO NWs have been used on LED devices (λ = 450 nm), which improved the light output power by 31 % at the current of 150 mA comparing to the one without NWs and did not deteriorate the electrical properties. Such ITO NWs open opportunity in LED devices to further improve light extraction efficiency. © 2016, Li et al.

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