Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308 nm were achieved using high density (2.5 × 10⁹ cm⁻²) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy and linear dependence of the intensity with varying excitation power. More significantly, the radiative recombination was found to dominant from 15 to 300 K, with a high internal quantum efficiency of 62% even at room temperature.

We report localised-surface-plasmon (LSP) enhanced deep-ultraviolet light-emitting diodes (deep-UV LEDs) using Al nanoparticles for LSP coupling. Polygonal Al nanoparticles were fabricated on the top surfaces of the deep-UV LEDs using the oblique-angle deposition method. Both the top- and bottom-emission electroluminescence of deep-UV LEDs with 279 nm multiple-quantum-well emissions can be effectively enhanced by the coupling with the LSP generated in the Al nanoparticles. The primary bottom-emission wavelength is longer than the primary top-emission wavelength. This difference in wavelength can be attributed to the substrate-induced Fano resonance effect. For resonance modes with shorter wavelengths, the radiation fraction directed back into the LEDs is largest in the direction that is nearly parallel to the surface of the device and results in total reflection and re-absorption in the LEDs.

According to first-principles calculations, the solubility of Mg as a substitute for Ga or Al in Al _x Ga_{1 – x} N bulk is limited by large, positive formation enthalpies. In contrast to the bulk case, the formation enthalpies become negative on Al _x Ga_{1 – x} N surface. In addition, the N-rich growth atmosphere can also be favorable to Mg incorporation on the surface by changing the chemical potentials. On the basis of these special features, we proposed a modified surface engineering technique that applies periodical interruptions under an ultimate V/III ratio condition (extremely N-rich), to enhance Mg effective incorporation. By optimizing the interruption conditions (2 nm interruption interval with 2 s interruption time), the enhancement ratio can be up to about 5 in the Al_0.99Ga_0.01N epilayer.