To improve the light extraction efficiency of InGaN-light emitting diode (LED), inverted hexagonal cone shaped air voids with {10–11} GaN crystal planes were formed between a patterned sapphire substrate and GaN epitaxial layer using a H3PO4-based hot chemical etching method. The air-voids embedded LED showed 12% and 210% higher optical power than a patterned substrate LED and a flat substrate LED, respectively. A ray tracing simulation revealed that the light extraction through the top face of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids.

The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.

The electrostatic discharge (ESD) properties of the InGaN-light emitting diode (LED) were investigated in terms of the internal capacitance of the InGaN-LED. The LEDs with higher internal capacitance were found to be more resistant to external ESD impulses. The internal capacitance of the InGaN-LED was controlled by the silicon doping level of the n-GaN layer bordering the active layer. The human body model ESD yield at −500 V was increased from 27% to 94% by increasing the internal capacitance. Moreover, the high ESD pass yield was maintained up to −7000 V.

Articles you may be interested inLight extraction improvement of InGaN light-emitting diodes with large-area highly ordered ITO nanobowls photonic crystal via self-assembled nanosphere lithography AIP Advances 3, 092124 (2013); 10.1063/1.4823478 InGaN/GaN nanorod array white light-emitting diode Appl. Phys. Lett. 97, 073101 (2010); 10.1063/1.3478515 The effect of the internal capacitance of InGaN-light emitting diode on the electrostatic discharge properties Appl. Phys. Lett. 94, 131106 (2009); 10.1063/1.3114974 The effect of the last quantum barrier on the internal quantum efficiency of InGaN-light emitting diode Selective area deposited blue GaN-InGaN multiple-quantum well light emitting diodes over silicon substrates

The temperature‐dependent device characteristics of InGaN/GaN near‐ultraviolet light‐emitting diodes, operating at λ ∼380 nm, with a chip size of 0.5 × 1 mm2 were reported. Their optical and spectral properties were measured and analyzed at different injection current levels and heatsink temperatures. The device performance showed the optical output power of 92.8 mW, forward voltage of 4.30 V, and emission peak wavelength of 380 nm at 350 mA and 298 K. The junction temperature (Tj) was experimentally estimated via the forward voltage method, leading to a thermal resistance of ∼10.03 K W−1. For comparison with the simulated Tj, the three‐dimensional steady‐state heat transfer simulation based on the finite element method was also carried out.