Wafer-scale Thermodynamically Stable GaN Nanorods via Two-Step Self-Limiting Epitaxy for Optoelectronic Applications.

We present a method of epitaxially growing thermodynamically stable gallium nitride (GaN) nanorods via metal-organic chemical vapor deposition (MOCVD) by invoking a two-step self-limited growth (TSSLG) mechanism. This allows for growth of nanorods with excellent geometrical uniformity with no visible extended defects over a 100 mm sapphire (Al2O3) wafer. An ex-situ study of the growth morphology as a function of growth time for the two self-limiting steps elucidate the growth dynamics, which show that formation of an Ehrlich-Schwoebel barrier and preferential growth in the c-plane direction governs the growth process. This process allows monolithic formation of dimensionally uniform nanowires on templates with varying filling matrix patterns for a variety of novel electronic and optoelectronic applications. A color tunable phosphor-free white light LED with a coaxial architecture is fabricated as a demonstration of the applicability of these nanorods grown by TSSLG.

Titanium oxide nanotube arrays for high light extraction efficiency of GaN-based vertical light-emitting diodes.

TiO2 nanotube (NT) arrays were fabricated on the surface of n-GaN through a liquid-phase conversion process using ZnO nanorods (NRs) as a template for high-efficiency InGaN/GaN multiple quantum well (MQW) vertical light-emitting diodes (VLEDs). The optical output power of the VLEDs with TiO2 NTs was remarkably enhanced by 23% and 189% at an injection current of 350 mA compared to those of VLEDs with ZnO NRs and planar VLEDs, respectively. The large enhancement in optical output is attributed to a synergistic effect of efficient light injection from the n-GaN layer of the VLED to TiO2 NTs because of the well-matched refractive indices and superior light extraction into air at the end of the TiO2 NTs. Light propagation along various configurations of TiO2 NTs on the VLEDs was investigated using finite-difference time domain simulations and the results indicated that the wall thickness of the TiO2 NTs should be maintained close to 20 nm for superior light extraction from the VLEDs.

Light-Emitting Diodes with Hierarchical and Multifunctional Surface Structures for High Light Extraction and an Antifouling Effect.

Bioinspired hierarchical structures on the surface of vertical light-emitting diodes (VLEDs) are demonstrated by combining a self-assembled dip-coating process and nanopatterning transfer method using thermal release tape. This versatile surface structure can efficiently reduce the total internal reflection and add functions, such as superhydrophobicity and high oleophobicity, to achieve an antifouling effect for VLEDs.

Enhanced optical output power of InGaN/GaN vertical light-emitting diodes by ZnO nanorods on plasma-treated N-face GaN.

Light-emitting diodes (LEDs) play an important role as a formidable contender for next-generation lighting sources and rapidly replace conventional lighting sources. In this report, the growth of high density inclined ZnO nanorods (NRs) on the N-face n-GaN surface for high efficiency vertical light-emitting diodes (VLEDs) is demonstrated based on oxygen plasma pretreatment and hydrothermal growth. Surface modification by oxygen plasma pretreatment efficiently produces GaOx nanoparticles on the N-face n-GaN surface and they play an important role in the hydrothermal growth of dense and inclined ZnO NRs. The optical output power of ZnO NR VLEDs following oxygen plasma pretreatment is strongly enhanced by a factor of 3.25 at an injection current of 350 mA, compared to that of planar VLEDs. The large enhancement of optical power is attributed to the dense ZnO NR layer which efficiently reduces the total internal reflection and enhances the waveguide effect in ZnO NRs.

Localized surface plasmon-enhanced near-ultraviolet emission from InGaN/GaN light-emitting diodes using silver and platinum nanoparticles.

We demonstrate localized surface plasmon (LSP)-enhanced near-ultraviolet light-emitting diodes (NUV-LEDs) using silver (Ag) and platinum (Pt) nanoparticles (NPs). The optical output power of NUV-LEDs with metal NPs is higher by 20.1% for NUV-LEDs with Ag NPs and 57.9% for NUV-LEDs with Pt NPs at 20 mA than that of NUV-LEDs without metal NPs. The time-resolved photoluminescence (TR-PL) spectra shows that the decay times of NUV-LEDs with Ag and Pt NPs are faster than that of NUV-LEDs without metal NPs. The TR-PL and absorbance spectra of metal NPs indicate that the spontaneous emission rate is increased by resonance coupling between excitons in the multiple quantum wells and LSPs in the metal NPs.