Micro-light-emitting diodes (μLEDs) are getting much attention in display industry because of their outstanding optical and electrical characteristics. μLEDs have several advantages over liquid crystal displays (LCDs) and organic lightemitting diodes (OLEDs). μLEDs are showing long lifetimes, high reliability, high power efficiencies, high brightness, and fast response times with tiny pixels. However, for commercial usage, the high production cost and low external quantum efficiency (EQE) are the major hurdles. In this review, we briefly discuss the breakthroughs in μLED technology, fabrication methods, optical/ electrical characteristics, and challenges for display applications. In addition, the development of monolithic μLEDs and general device characteristics combined with various quantum dot patterning processes are systematically discussed. Potential solutions to address these challenges are also presented case by case.

In this study, the effect of ITO contact ratio for blue light micro-light-emitting diode (µLED) with dimensions 40 μm × 40 μm was assessed. The contact ratio from 0.2 to 0.8 was designed for the ratio of electrode area to light-emitting area. As the contact ratio increased from 0.2 to 0.8, the turn-on voltage of µLED decreased. It could be due to the short lateral diffusion length in multiple quantum wells (MQW) and lower parallel resistance for the µLED with a large contact ratio. The leakage currents of single µLED were below 5.1 × 10–9 A, no matter the contact ratio. It means that the contact ratio does not affect the leakage current as measured on single chip. Moreover, µLED array with a 0.8 contact ratio presented the highest output power than other samples (5.25 mW as the current density of 1875 A/cm2). It could attribute to the MQWs usage, the metal contact reflective behavior and less current crowding, which generated more carriers and extracted more lighting from the µLED. The simulation data using SpeCLED software agreed well with these experiments, and µLED with a 0.8 contact ratio showed the best optoelectronic properties.

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