We investigated the hole injection mechanism in InGaN/GaN blue light-emitting diodes by growing monolithic dual-wavelength multiple-quantum-wells and measuring the electroluminescence spectra at different current densities under room temperature. By analyzing the spectral competition from quantum wells at different vertical locations, the hole injection depth was quantitatively measured. During the epitaxial growth, large size V-shape pits with 200–330 nm diameter were intentionally formed in the active region by controlling the growth condition. It was found that such defect has a significant influence on the hole injection depth. With large V-shape pits and reduced quantum barrier thickness, the hole can be injected beyond 8 pairs of quantum well/quantum barrier. And less “droop” effect at large current density were observed. A carrier transport model with the presence of large V-shape pits is established.

Microcavities with whispering gallery modes (WGM), usually formed by two-dimensional (2D) circular structures, are significant elements in integrated optics, quantum information, and topological photonics. We report three-dimensional (3D) WGM from self-bent-up microdisks consisting of strain-released AlGaN/GaN bilayers, which provide an extra degree of freedom of the WGM photons in the vertical dimension, in contrast with the 2D WGM whose field mainly distributes in the horizontal plane. Despite the ultrathin and deformed cavity layer, the 3D WGM shows a reasonably high quality factor for GaN-based microdisks (∼1300) and exhibits single mode lasing due to the anisotropic feature of the bent-up disk, a unique advantage over the conventional planar microdisks of the same material and size. Such devices provide altitude dependence of emitting direction and are promising for applications in multilevel integrated photonics circuits.

In this work, we have successfully fabricated microtubes by strain-induced self-rolling of a InGaN/GaN quantum wells nanomembrane. Freestanding quantum wells microtubes, with a diameter of 6 µm and wall thickness of 50 nm, are formed when the coherently strained InGaN/GaN quantum wells heterostructure is selectively released from the hosting substrate. Periodic oscillations due to whispering-gallery modes resonance were found superimposed on photoluminescence spectra even at low optical excitation power. With increasing pumping power density, the microtube is characterized by a stimulated emission with a threshold as low as 415 kW/cm. Such emission shows predominant TM polarization parallel to the microtube axis.

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.

We demonstrated a method to obtain super flexible LEDs, based on high quality pyramid arrays grown directly on sapphire substrates. Laser lift-off (LLO) and dual transfer processes were applied to transfer pyramid arrays face up onto the flexible substrates, which is more efficient than back light emission. Ag grid and Ag nanowires were employed as the electrical connection. No significant performance reduction appeared until the device reached a curvature radius of 0.5 mm. The performance reduction results from cracks appearing at the junction of the Ag grid, which can be improved by replacing the Ag grid with a strip electrode.

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We demonstrated surface-plasmon (SP) enhanced green light-emitting diodes (LEDs). Three types of Ag nanorod arrays with a minimum distance between the quantum well (QW) and Ag of 20, 40, and 55 nm respectively were fabricated on p-GaN layer. Photoluminescence measurements showed ∼175% emission enhancement for the 20 nm spacing while almost no enhancement for the 55 nm spacing. Simulation result showed that a localized surface plasmon resonance (LSPR) at a wavelength of ∼500 nm generated by Ag nanorod arrays induced InGaN/GaN QW and SP coupling. However, the electrical field of the LSPR generated by Ag nanorods only spread ∼40 nm in the vertical direction in GaN. This simulation result well explains the observation of SP-QW coupling emission enhancement for 20 nm spacing between Ag and QW, and the lack of enhancement for the 55 nm spacing samples.

We investigated the carrier injection mechanism in InGaN/GaN blue light-emitting diodes by growing monolithic dual-wavelength multiple quantum wells and measuring electroluminescence spectra at different current densities at room temperature. During the epitaxial growth, V-defects of different sizes were intentionally formed in the active region area by controlling the growth conditions. We found that the size of the V-defects has a significant effect on the spectral competition of dual-wavelength emissions. With small V-defects, light emitted from quantum wells near p-GaN is dominant. In a sample with large V-defects, quantum wells near n-GaN contribute more to carrier recombination. The hole injection depth of eight pairs of quantum wells far from p-GaN is quantitatively estimated. We attribute the different behaviors to the modulation of carrier injection depth by the formed V-defects.