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Abstract: High quality blue, green and yellow LEDs comprised of stable indium-rich clusters in InGaN/GaN multiple quantum wells (MQWs) have been successfully grown by metal-organic chemical vapor deposition. We show that the common degradation phenomenon on crystallinity can be avoided by these quasi-quantum dots as obtained from the integrated results of high resolution transmission electron microscopy (HRTEM), rocking curve and ω-scan analysis. Ultra-small sized indium clusters of 2 nm, 2.5 nm and 3 nm in diameter have been observed in the quantum wells from HRTEM analysis. We also show that by well controlling the dot size in the active layers, emitting wavelength in full visible light spectrum is achieved. In addition, several interesting observations were also found during analysis. First, the propagation of threading dislocations would be efficiently stopped by the quasi-dots, which behave as real quantum dots. Secondly, the thickness dependence of phase separation has also been demonstrated in the sample emitting blue light where the quantum well thickness ranges in 1.7∼2 nm and nominal In content is in 8∼10% regime. Thirdly, the phase separation is independent of film polarity (Ga-polarity or N-polarity). [Copyright &y& Elsevier]

Abstract: The optical performance of blue-light emitting GaN is greatly influenced by the density and distribution of threading dislocations (TDs), which can be reduced and controlled by varying the ratio of mask-to-window width during epitaxial lateral overgrowth (ELOG). Here we study the evolution of microstructure and optical property along with the spatial distribution of defects in ELOG GaN films by varying the fill factor (FF), defined as mask-to-window width ratio, which was varied from one to five while the window width was maintained at 5μm. We employed a two-step ELOG method for this study by way of metal organic chemical vapor deposition, where SiO2 was used as the mask and grown on a low-temperature grown GaN layer, which acted as the buffer and seed layer on a sapphire substrate. The patterns were comprised of circular dot arrays arranged along the 〈11¯00〉 directions of the underlying GaN and developed by the conventional photolithography method. X-ray rocking curves show that all the resulting films are of excellent epitaxial quality, of which the sample with FF=5 exhibits the best quality from the narrowest peak broadening. Cathodoluminescence spectra show the near bandgap UV emission as well as a yellow emission, which could have arisen from TDs. Transmission electron microscopy results show that the TDs emerging through the windows can be effectively impeded by the mask and bent toward the faceted planes of GaN pyramid islands. [Copyright &y& Elsevier]

A facile method for fabricating blue light-emitting diodes (B-LEDs) with small embedded quantum dots (QDs) and enhanced light emission is demonstrated by tuning the temperature of the growing GaN capping layer to eliminate V-defects. As the growth temperature increases from 770 °C to 840 °C, not only does the density of the V-defects reduce from 4.12 ∗ 10 8 #/cm 2 nm to zero on a smooth surface, but the QDs also get smaller. Therefore, the growth mechanism of smaller QDs assisted by elimination of V-defects is discussed. Photoluminescence and electroluminescence results show that smaller embedded QDs can improve recombination efficiency, and thus achieve higher peak intensity with smaller peak broadening. Accordingly, the external quantum efficiency of the B-LEDs with smaller QDs is enhanced, leading to a 6.8% increase in light output power in lamp-form package LEDs. [ABSTRACT FROM AUTHOR]

Carrier concentration in a piezoelectric semiconductor greatly affects alternating current (AC) piezoelectric nanogenerators (NGs) because of the carrier screening effect on the piezoelectric potential. The output performance of a series of NGs is investigated by tuning the Si dopant concentration in GaN nanowires. The results show a strong carrier screening effect that degrades output performance for high doping concentrations but results in high output power for low doping concentrations. [ABSTRACT FROM AUTHOR]

Highlights: [•] A simply fabricated platform for high efficiency plasmonic LED is demonstrated. [•] Blue light emission is increased by 4.4-fold via localized surface plasmon coupling. [•] A 1.5-fold higher spontaneous emission rate confirms the fast recombination channel. [•] 53% enhancement in internal quantum efficiency was performed. [Copyright &y& Elsevier]

Freestanding wurtzite GaN nanoprotruded microbelts with GaO core, with typical thickness 1-10 μm, and length of few millimeters are synthesized by thermal annealing of Ga metal and subsequent reaction with ammonia at a low flow rate. They are of distinctive rectangular shape with a typical width of 10-100 μm. Thickness of the belt is about 1/10th of the width and length up to a few millimeters. The GaN, GaO layers and the GaN-GaO interface are characterized by high-resolution transmission electron microscopy after focused ion beam sectioning of the belt. Initially, GaO nucleates after reaction with the O available in the environment, and subsequent reaction with NH results in the formation of core-shell structure in the catalyst-free vapor-solid growth process. Having a low-symmetry phase, GaO can grow only in certain preferred directions thus controlling the final morphology of the belt. Nanoscale protrusions ~50-100 nm found on the surface of the belts could be an ideal system for building functional devices. [ABSTRACT FROM AUTHOR]

In article number 1400392, Chuan‐Pu Liu and co‐workers report the synthesis of Si‐doped GaN nanowire arrays with various carrier concentrations to investigate the impact of carrier screening on the output performance of alternating‐current (AC) vertical integrated nanogenerators (VINGs). The output voltage and current density of AC VINGs strongly decrease with increasing doping concentration. Consequently, AC VINGs can be optimized if they are composed of piezotronic materials with the lowest possible carrier concentration to prevent the screening effect. [ABSTRACT FROM AUTHOR]