The distributions of the electroluminescence of AlGaInP-based flip-chip red light-emitting diodes with a size of $100\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ have been obtained via microscopic hyperspectral imaging by capturing spatially resolved light emission from the side of a transparent substrate. As the injected DC current exceeds the current corresponding to the maximum external quantum efficiency, the light emission from the current crowding region decreases due to the self-heating effect, whereas the emission of the region corresponding to the anode becomes dominant due to the low heat resistance.

The optical and chromatic characteristics of InGaN-based micro-light-emitting diodes (micro-LEDs) grown on silicon substrates with blue, green, and red emissions have been investigated. The red micro-LEDs exhibited a large full-width at half maximum and a strong blueshift upon increasing current density. The 20 μm blue, green, and red micro-LEDs achieve a maximum external quantum efficiency of 8.2% at 2.65 A/cm2, 5.1% at 5 A/cm2, and 0.62% at 0.1 A/cm2, respectively, which is superior to their 8 μm counterparts. The dependences of a color gamut on the temperature and current density of InGaN-based tri-color micro-LEDs can provide guidance for improving the performance of full-color micro-LED displays.

Electrical-chromatic characteristics of red, green, and blue micro-LEDs ( $10\times 10\,\,\mu \text{m}$ ) are investigated at temperatures ranging from 300 to 340 K. The external quantum efficiency (EQE) of red micro-LEDs decreases significantly with the increasement in temperature, suggesting that heat dissipation is crucial for red micro-LEDs. The impacts of temperature and driving current on the chromaticity coordinates of the light emission from micro-LEDs are determined. When the trichromatic micro-LEDs are driven by the currents corresponding to the maximum EQE, the influence of temperature on the color gamut is limited, facilitating the achievement of high color gamut and high efficiency.

The anomalous droop in the external quantum efficiency (EQE) induced by the localization of excitons in GaN/InGaN green micro-light-emitting diodes (micro-LEDs) has been demonstrated at temperatures ranging from 25 to 100 K. At cryogenic temperatures, the random distribution of excitons among local potential energy minima limits the radiative recombination and reduces the EQE of green micro-LEDs. As the temperature increases from 25 to 100 K, the hopping of excitons from shallow potential energy minima to the potential energy valley contributes to the enhancement of radiative recombination. The distribution of excitons among local potential energy minima at cryogenic temperatures is also affected by the current density due to the influence of Coulomb screening of the polarization field and the band-filling effect.

This study aimed to investigate the impact of mesa geometry on the light output characteristics of AlGaN-based 275 nm deep ultraviolet light-emitting diodes (DUV-LEDs). By dividing the original single-junction mesa into four parts and connecting them serially (four-in-one), high-voltage (HV) DUV-LEDs with rectangular, hexagonal, circular, triangular, and square submesas were realized, achieving significant enhancement of the light output power (LOP) and wall-plug efficiency (WPE). The LOP of HV DUV-LEDs with hexagonal submesas has been promoted substantially compared to that of the original DUV-LEDs. Among the investigated five different types of submesas, hexagonal-type HV DUV-LEDs can achieve the highest LOP and WPE due to the higher sidewall light extraction. Furthermore, it is also demonstrated that pulse current driving can reduce the self-heating effect of HV DUV-LEDs.

By using microscopic hyperspectral imaging, the inhomogeneous electroluminescence (EL) across the mesa of blue vertical micro-LEDs has been investigated. The sidewall emission dominates the EL of micro-LEDs under higher current injections and that bright circular light emission from the sidewall region possesses larger peak energy due to the strain relaxation. The multi-channel radiative recombination leads to the high-energy peaks in the EL spectra of the inner and dim regions of mesa. The photons, which are generated in the inner region of mesa and transported to sidewall after experiencing multiple reflections, act as the indispensable component for sidewall emissions. This work emphasizes the importance of spatially resolved spectral characterization in revealing the mechanisms of light emission from sidewall of micro-LEDs.