GaN growth on cone-shaped nanoscale patterned sapphire substrates (NPSS) in the initial stages was investigated via a series of growth interruptions. The thickness of the nucleation layer (NL) was optimized as 15 nm. A high-quality GaN film was achieved with an average surface roughness of 0.13 nm over 5 × 5 μm², a threading dislocation density (TDD) of 1.80 × 10⁸ cm⁻² and a residual stress of 0.40 GPa. X-ray diffraction (XRD) ω/φ-scans, cathodoluminescence (CL) mapping and transmission electron microscopy (TEM) measurements were carried out to study the GaN coalescence process on NPSS. Nano-nucleating, lateral growth and the submerging of the large tilt grains were confirmed as the primary factors that reduced the TDD and residual stress. The mechanism for GaN nucleation on NPSS and its effect on the subsequent growth stages were elucidated.

A volcano-shaped nano-patterned sapphire substrate (VNPSS) was fabricated by nanoimprint lithography and wet etching. The edge effects were used to form a ring mask for wet etching. The widths of the SiO₂ rings were obtained as 136 and 91 nm by changing the reactive ion etching time. The crystal planes were determined to be {10} and {10} for the etching facets of the outside and inside of the ring, respectively. X-ray diffraction rocking curves indicate that the dislocation density of the GaN epilayer on the VNPSS is lower than that on the nano-patterned sapphire substrate (NPSS). Temperature-dependent photoluminescence results show that the internal quantum efficiency of the GaN-based light emitting diode (LED) on the VNPSS is 24% larger than that on the NPSS, which is due to the improved crystal quality. 3-D finite difference time domain (FDTD) simulations show that the light extraction efficiency (LEE) of the GaN-based LED on the VNPSS is 21% more than that of the LED on the NPSS, which conforms to the LEE enhancement by PL measurement. The use of edge effects provides ideas for preparing complex NPSS patterns with commonly used imprint stamps to further increase crystal quality and LEE.

We analyzed the coupling behavior between the localized surface plasmon (LSP) and quantum wells (QWs) using cathodoluminescence (CL) in a green light-emitting diodes (LED) with Ag nanoparticles (NPs) filled in photonic crystal (PhC) holes. Photoluminescence (PL) suppression and CL enhancement were obtained for the same green LED sample with the Ag NP array. Time-resolved PL (TRPL) results indicate strong coupling between the LSP and the QWs. Three-dimensional (3D) finite difference time domain (FDTD) simulation was performed using a three-body model consisting of two orthogonal dipoles and a single Ag NP. The LSP–QWs coupling effect was separated from the electron-beam (e-beam)–LSP–QW system by linear approximation. The energy dissipation was significantly reduced by the z-dipole introduction under the e-beam excitation. In this paper, the coupling mechanism is discussed and a novel emission structure is proposed.

Localized surface plasmon (LSP) coupling with many radiators are investigated. The LSP is generated by excitation of laser or electron beam on the random Ag nano particles (NPs) and arrayed ones embedded in the p-GaN of green LEDs. They couple with the excitons or radiative recombination in the quantum well (QW) and electron beam, which enhance or suppress the luminescence of the radiators. The photoluminescence (PL) intensity of periodic Ag NPs can get as much as 4.5 times higher than that of bare LED. In addition to the periodic structure, the morphology of Ag NPs also affects the localized SP (LSP) resonance intensity and light scattering efficiency. In the finite difference time domain (FDTD) simulation, five x-polarized dipoles are approximated to five quantum wells. Considering the interaction between the five dipoles and their feedback effect on LSP, the enhancement effect of SP dipole coupling with Ag NPs is amplified and the energy dissipation is reduced. The enhancement of cathodoluminescence (CL) was also found in green LEDs with Ag NPs. The three-body model composed of two orthogonal dipoles and an Ag NP is used for 3D FDTD simulation. The LSP-QWs coupling effect is separated from the electron beam (e-beam)-LSP-QW system by linear approximation. Under the excitation of electron beam, the introduction of z-dipole greatly reduces the energy dissipation. In the cross-sectional sample, z-polarized dipoles in QWs show more coupling strength to the dipole and quadrupole modes of LSP. The perturbation theory is used to separate the LSP coupling effects to x-dipole and z-dipole. At last, the resonator and the antenna effects are discussed for LSP coupling at different positions to the Ag NP.

Ag nanoparticles (NPs) are filled in a photonic crystal (PhC) hole array on green light emitting diodes (LEDs). The localized surface plasmon (LSP)–quantum well (QW) coupling effect is studied by measuring the cathodoluminescence (CL) spectra impinging at the specific spots on the Ag NPs. Twenty-six percent and fifty-two percent enhancements of the CL intensities are obtained at the center and edge of the Ag NP, respectively, compared to the result that the electron-beam (e-beam) excites the QW directly. To illustrate the coupling process of the three-body system of e-beam–LSP–QW, a perturbation theory combining a three-dimensional (3D) finite difference time domain (FDTD) simulation is put forward. The effects of the polarization orientation of the dipole and the field symmetry of the LSP on the LSP–QW coupling are also discussed.

The three-dimensional thermal characteristics of micro-light-emitting diodes (μLEDs) on GaN and sapphire substrates were studied with forward-voltage methods, thermal transient measurements, and infrared thermal imaging. The μLEDs on the GaN substrate showed an approximately 10 °C lower junction temperature and smaller amplitude of the K factors than those on the sapphire substrate under the current injection level of 4 kA cm⁻². The thermal transient measurement showed that the spreading thermal resistances of the mesa, the GaN epilayer, and the interface of the GaN/substrate were reduced significantly for μLEDs on the GaN substrate because of the high-quality GaN crystal and the homogeneous interfaces. The infrared thermal images showed lower total average junction temperatures and more uniform temperature distributions for the μLEDs on the GaN substrate, which were also simulated with APSYS software. The thermal transport mechanisms are discussed for the lateral and vertical directions in the μLEDs.