Search

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.

Underwater visible light (UVLC) system based on a single transceiver-integrated micro-light-emitting diode (μLED) pixel, especially μLED devices suitable for this multifunctional application, were rarely reported. This study improved the external quantum efficiency and modulation bandwidth of green μLEDs by using an InGaN pre-layer to mitigating lattice mismatch and minimizing quantum confined stark effect. Moreover, pre-layer region increased absorbed optical length and the photogenerated carriers in this region were screened from radiation recombination, which significantly increased the responsivity of the μLED PD when turned on. At 3.9 V bias, remarkable responsivity up to of 0.42 and 0.14 A/W for 405 and 450 nm were obtained, respectively. The increased thickness of the active region also leads to a decrease in the junction capacitance and improves the receiving bandwidth. Based on the transceiver performance improvement, we developed a 1.05 Gbps full-duplex UVLC system with single green μLED simultaneously acting as receiver and transmitter for the uplink and downlink, respectively. The single μLED functioned similar to an underwater transceiver antenna. The device achieved a power-conversion efficiency of 14.7% for blue light when used as a photovoltaic cell. Thus, this multifunctional μLED can facilitate the realization of miniaturized underwater optical antennas with low power consumption and high integration.

Optical crosstalk between adjacent pixels acts as one of the major challenges for miniaturized light-emitting diode (mini-LED) displays. In this letter, the impacts of optical crosstalk on the chromatic characteristics of the four-in-one mini-LED integrated matrix device (IMD) have been investigated. The influence of driving current on the optical crosstalk in four-in-one IMDs has also been determined. To be specific, red mini-LEDs can compromise the color gamut of full-color self-emissive mini-LED displays. This demonstrates the crucial need to optimize the operating conditions of red mini-LEDs to alleviate optical crosstalk in displays using four-in-one IMDs. $\Delta u$ ’v’, the chromatic shift, causing by the optical crosstalk originating from red mini-LEDs reaches 0.024 and 0.045 for green and blue mini-LEDs, and the color gamut decreases from 112.00% to 102.47% under the red crosstalk.

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.