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Considering the low electrical conductivity of the p-type contact layer, current crowding is the primary impediment to the preparation of gallium nitride green micro-light-emitting-diodes (micro-LEDs). In this study, the effects of different p-electrode contact area ratios on the photoelectric characteristics of green micro-LEDs were investigated. We demonstrated that appropriately increasing the p-electrode contact area ratio improves the photoelectric performance of green micro-LEDs, including the dynamic resistance, electroluminescence (EL) intensity, light output power (LOP), wall-plug efficiency (WPE), and external quantum efficiency. Microscopic hyperspectral imaging ( $\mu $ -HSI) revealed that optimizing the p-electrode contact area ratio promotes current spreading and improves the uniformity of luminous distribution on chip surfaces. The Comsol Multiphysics simulation shows the distribution of current density at four kinds of contact area ratios. The green micro-LEDs with p-electrode contact area ratios of 30% demonstrated the best photoelectric performance and uniform luminous distribution.

Polarization effects introduced by the electron-blocking layer (EBL) in InGaN-based micro light-emitting diodes ( $\mu $ LEDs) have a significant impact on their display and detection applications. Therefore, the impact and necessity of EBL structure for $\mu $ LED devices intended for such applications need to be reassessed. This article investigates the effect of removing p-AlGaN EBL structure on the performance of blue $\mu $ LEDs when used as light-emitting devices under low-current injection and photodetectors (PDs). Luminescence efficiency and color stability of the $\mu $ LED without EBL improve under low-current injection due to weakened polarization-induced band-bending and enhanced hole injection and electron confinement, as numerical simulations show. For photodetection applications, removing EBL reduces the photogenerated carrier escape barrier, improving the responsivity and bandwidth of $\mu $ LED PDs. Additionally, anomalous responsivities, dependent on bias and excitation energy, were observed in $\mu $ LED PDs with EBL. These observations can be elucidated by the trap-assisted tunneling (TAT) mechanism.

Given the growing interest in micro-scale thermal management of mini- and micro-light-emitting diodes (LEDs), it is crucial to develop an effective 2-D junction temperature measurement method. In this article, the microscopic hyperspectral imaging ( $\mu $ -HSI) technique has been proposed to probe the 2-D photo-thermal distribution of the flip-chip mini-LEDs. Running on a two-axis rotating platform, $\mu $ -HSI is able to directly focus on the epitaxial layer surface (episurface) and lateral side of the LED chips to acquire their 2-D spectral distributions. Subsequently, the full width at half maximum (FWHM) matrix was extracted to deduce the 2-D junction temperature distributions. As a result, the location and temperature distribution of the active layer, i.e., p-n junction, can be determined accurately. The mean temperature of the episurface approximately matches that of the active layer. The Raman shift method was applied to verify the accuracy of the $\mu $ -HSI technique. In addition, the extra fine structures as well as temperature distributions of the interface between the episurface and sapphire or electrodes are distinguished and analyzed by this technique. This work offers an effective tool for the quality improvement and thermal management of mini-LEDs.