AlGaN Ultraviolet Micro-LEDs

Abstract

AlGaN-based UV LEDs have proven to have broad applications in many fields including sterilization, disinfection, purification, and phototherapy, but the performance still needs to be further improved. Benefiting from advantages such as better current spreading, lower self-heating effect and higher light extraction efficiency achieved by the reduced LED size, UV micro-LEDs are expected to improve quantum efficiency and thus can expand more potential applications. In this article, performance enhancement techniques and applications of UV micro-LEDs will be reviewed, providing an outlook for further development of AlGaN-based UV-LEDs. The micro-LED format offers possibilities to address fundamental issues that UV LEDs confront in general, but also demonstrates specific characteristics and performance advantages opening up new areas of application including high-speed optical communication, time-resolved fluorescence lifetime measurement, optical pumping, direct writing and charge management.

The micro-LED roadmap: status quo and prospects

“…Compared with broad-area LEDs, AlGaN UV micro-LEDs with typical size from 1 µm to 100 µm have advantages of array format, better current spreading, lower thermal effect, higher sustainable current density, higher modulation bandwidth, higher light extraction efficiency, and higher density of LOP, which can address fundamental device or system issues and thus open up more applications. Figure 8 summarizes the applications of broad-area UV LEDs such as air disinfection, curing, sensing and photo therapy, as well as the advanced UV micro-LED applications including micro-LED display, optical communication, maskless photolithography, time-resolved fluorescence detection and charge management [63].…”

“…UV micro-LEDs are expected to demonstrate significant advantages of high efficiency, high reliability, fast modulation speed, low cost and low-power consumption. However, the EQE of UV LEDs is still low, especially below 20% at UVC range [63,70]. The crystal quality by MOCVD growth, high-quality p-type AlGaN layer, UV light absorption inside the UV LED device are typical limiting factors, and researches of UV micro-LED efficiency are far less than visible micro-LEDs, e.g.…”

“…High-quality material growth and device fabrication are the first step to conquer these challenges. UV LED structure have been optimized to increase the IQE and light extraction efficiency [63]. Mg-delta doping and Mg-doped SL have been employed to increase the p-doping efficiency in AlGaN.…”

The dependence of light extraction improvement on optimized surface microstructure for AlGaN-based UVC-LEDs considering TM-polarized emission

“…Ultraviolet (UV) light has a wide range of applications or potential applications in non-line-of-sight (NLOS) UV-communication, water purification, UV curing, medical treatment, plant lighting, optical sensing, lithography and other fields [1][2][3][4][5][6]. Especially the UVC (200-280 nm) part of the solar spectrum is strongly attenuated in the earth's atmosphere, which brings about an almost interference free space atmospheric channel and a no defense mechanism for organisms to high-energy photon exposure.…”

Size dependent characteristics of AlGaN-based deep ultraviolet micro-light-emitting-diodes

“…There are only a few reports on the size dependence of DUV LEDs characteristic. [13][14][15][16][17] Micro-LEDs (μLEDs) have been shown to increase the LEE in visible LEDs, 18,19) so it is worth exploring the effect of device size on DUV LED LEE. Additionally, fabricating LEDs with smaller mesas can reduce the forward voltage and mitigate the current crowding present in large UV LEDs, since growing thick and conductive (<10 mΩ cm) n-AlGaN remains a challenge.…”