No abstract

In this paper, the GaN-based green 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 EQE droop phenomenon, luminance and output power density characteristics were depicted up to the highest current density injection condition to date (120 kA/cm2), and 6 μm device exhibited an improved EQE performance with the peak EQE value of 16.59% at 20 A/cm2 and over 600k and 6M cd/cm2 at 1 and 10 A/cm2, 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 (EL) spectra and converted to CIE 1931 color space. The whole shifting track and color variation from 1 A/cm2 to 120 kA/cm2 were demonstrated by color coordinates.

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.