Min Jiang

Size-dependent efficiency degradation remains a major challenge for deeply scaled GaN-based micro-light-emitting diodes (micro-LEDs) because etched sidewalls increasingly influence carrier recombination. Here, square micro-LEDs with lateral dimensions of 5–50 μm were fabricated from the same plasma-assisted molecular-beam-epitaxy-grown wafer containing a five-period InGaN quantum-well/1 nm Al_0.1Ga_0.9N interlayer/InGaN quantum-dot-like (QW–QD) composite active region. Contrary to the conventional size effect, the light output power density and external quantum efficiency (EQE) increased as the mesa size decreased. The peak EQEs were 3.66%, 4.53%, 5.63%, 7.04%, and 7.27% for the 50, 40, 30, 10, and 5 μm devices, respectively, corresponding to an approximately 98.6% increase from 50 to 5 μm. The favorable scaling is consistent with localization-mediated suppression of lateral carrier loss combined with size-dependent light extraction. The present measurements do not quantitatively separate injection, internal efficiency, and extraction contributions. These results demonstrate the potential of ultrathin-interlayer QW–QD active-region engineering for scaled GaN micro-LEDs.

Due to the emerging requirements of miniaturization and multifunctionality, monolithic devices with both functions of lighting and detection are essential for next-generation optoelectronic devices. In this work, based on freestanding (In,Ga)N films, we demonstrate a monolithic device with two functions of lighting and self-powered detection successfully. The freestanding (In,Ga)N film is detached from the epitaxial silicon (Si) substrate by a cost-effective and fast method of electrochemical etching. Due to the stress release and the lightening of the quantum-confined Stark effect (QCSE), the wavelength blueshift of electroluminescent (EL) peak is very small (Q = 821) for self-powered detection, leading to the excellent detection selectivity. The main reason can be attributed to the removal of Si by the lift-off process, which can limit the response to visible light. This work paves an effective way to develop new monolithic multifunctional devices for both detection and display.

Underwater wireless optical communication (UWOC) is a wireless communication technology using visible light to transmit data in an underwater environment, which has wide applications. Based on lift-off (In,Ga)N nanowires, this work has proposed and successfully demonstrated a self-powered photoelectrochemical (PEC) photodetector (PD) with excellent transmissivity. The transparent functionality of the PD is critical for 360° omnidirectional underwater detection, which was realized by detaching the (In,Ga)N nanowires from the opaque epitaxial substrates to the indium tin oxide (ITO)/glass. It was also found that the insulating SiO₂ layer can enhance the photocurrent by about 12 times. The core–shell structure of the nanowires is beneficial for generating carriers and contributing to the photocurrent. Furthermore, a communication system with ASCII code is set to demonstrate the PD detection in underwater communication. This work paves an effective way to develop 360° omnidirectional PDs for the wide applications in UWOC system and underwater photodetection.