Developing aluminium gallium nitride deep-ultraviolet (UVC) micro-light-emitting diodes (micro-LEDs) with sufficient power has been a challenge, which particularly limits these devices to various applications. However, advanced fabrication processes have been developed to enable the demonstration of highly efficient 270 nm UVC micro-LEDs and large-format UVC micro-LED displays with high resolution for maskless photolithography. Optical and electrical characterizations were performed on UVC micro-LEDs with sizes ranging from 3 µm to 100 μm to evaluate these emerging devices. The 3 μm device achieved a record-high peak external quantum efficiency of 5.7% and a maximum brightness of 396 W cm^–2. Moreover, 2,540 pixels per inch parallel-connected UVC micro-LED arrays featuring rear-side reflection layers exhibited emission uniformity and collimation. UVC micro-LED displays, with a resolution of 320 × 140, were explicitly designed for maskless photolithography applications utilizing a customized integrated circuit driver for optimal performance. The UVC micro-LEDs and UVC micro-displays provide sufficient doses to fully expose the photoresist film within seconds, owing to their enhanced current spreading uniformity, improved heat dispersion and superior light extraction efficiency. This work may open a path to maskless photolithography, potentially leading to revolutionary developments in the semiconductor industry.

In this paper, the GaN-based green micro light-emitting diodes (Micro-LEDs) with various sizes (from 3 to 100 μm) were fabricated and electro-optically characterized. Atom layer deposition (ALD) passivation and potassium hydroxide (KOH) treatment were applied to eliminate the sidewall damage. The size dependence of Micro-LED was systematically analyzed with current-versus-voltage and current density-versus-voltage relationship. According to the favorable ideality factor results (<1.5), the optimized sidewall treatment was achieved when the device size shrank down to <10 μm. In addition, the external quantum efficiency (EQE) droop phenomenon, luminance and output power density characteristics were depicted up to the highest current density injection condition to date (120 kA cm⁻²), and 6 μm device exhibited an improved EQE performance with the peak EQE value of 16.59% at 20 A cm⁻² and over 600k and 6M cd cm⁻² at 1 and 10 A cm⁻², indicating a greater brightness quality for over 3000 PPI multiple display application. Lastly, the blue shift of 6 μm device with elevating current density was observed in electroluminescence spectra and converted to CIE 1931 color space. The whole shifting track and color variation from 1 A cm⁻² to 120 kA cm⁻² were demonstrated by color coordinates.

In this paper, we report high-performance Micro-LEDs on sapphire substrates, with pixel size scaling to 20 µm and an ultra-high current density of 9902 A/cm². The forward voltages (V_F) of the devices ranged from 2.32 V to 2.39 V under an injection current density of 10 A/cm². The size and structure-dependent effects were subsequently investigated to optimize the device design. The reliability of Micro-LED devices was evaluated under long-aging, high-temperature, and high-humidity conditions. It was found that Micro-LED devices can maintain comparable performance with an emission wavelength of about 445 nm and a full width at half maximum (FWHM) of 22 nm under extreme environments. Following this, specific analysis with four detailed factors of forward voltage, forward current, slope, and leakage current was carried out in order to show the influence of the different environments on different aspects of the devices.

Ultraviolet band C (UV-C) micro light-emitting diodes (micro-LEDs) provide a high energy light emission of 200–280 nm, which are brilliantly utilized in optogenetics, communications, and fluorescence. However, the limited device efficiency notably restricts the grand potential application field. In this work, three types of 20 × 20 μm² UV-C micro-LEDs with the peak wavelength of 269 nm are fabricated by different etching strategies, including an inductively coupled plasma (ICP), post-ICP tetramethylammonium hydroxide, and a hybrid scheme combining plasma and chemical treatment. By enhancing the radiative recombination and light extraction, the hybrid scheme improves the peak external quantum efficiency of UV-C micro-LEDs to 3.45%, an elevation of 57.5% compared with ICP. A step advance in the forward injection current and ideality factor is also found on the devices fabricated by the hybrid scheme due to better contact on the AlGaN surface.

We present a significant enhancement of internal quantum efficiency (IQE) exceeding 90% in InGaN-based Micro-light-emitting diodes (Micro-LEDs) achieved through sidewall passivation using atomic layer deposition (ALD). An intriguing observation is an inverse correlation between the diode ideality factor and IQE; devices boasting over 90% IQE consistently exhibit a diode ideality factor below 1.5. Specifically, for 10- $\mu $ m-sized devices, an IQE of 95.6% paired with a remarkably low ideality factor of 1.27 is realized, representing the pinnacle of achievable IQE at room temperature. In addition, enhanced light extraction efficiency (LEE) is observed through a low-refractive-index dielectric layer for passivation, facilitating a large critical angle at the interfaces. However, despite these advancements, the LEE for passivated devices remains at approximately 26%, resulting in an external quantum efficiency (EQE) of 25%. Consequently, our findings strongly advocate further device performance improvements in Micro-LEDs by enhancing LEE, necessitating novel device structures. In addition, we report the groundbreaking verification of the unity ideality factor for radiative recombination current in InGaN-based Micro-LEDs. This achievement is realized through the isolation of the radiative current component from the total current, thus substantiating the legitimacy of employing the Shockley-Read–Hall (SRH) to analyze the electrical characteristics of InGaN Micro-LEDs.