Overcoming the fundamental light-extraction efficiency limitations of deep ultraviolet light-emitting diodes by utilizing transverse-magnetic-dominant emission

Abstract

While the demand for deep ultraviolet (DUV) light sources is rapidly growing, the efficiency of current AlGaN-based DUV light-emitting diodes (LEDs) remains very low due to their fundamentally limited light-extraction efficiency (LEE), calling for a novel LEE-enhancing approach to deliver a real breakthrough. Here, we propose sidewall emission-enhanced (SEE) DUV LEDs having multiple light-emitting mesa stripes to utilize inherently strong transverse-magnetic polarized light from the AlGaN active region and three-dimensional reflectors between the stripes. The SEE DUV LEDs show much enhanced light output power with a strongly upward-directed emission due to the exposed sidewall of the active region and Al-coated selective-area-grown n-type GaN micro-reflectors. The devices also show reduced operating voltage due to better n-type ohmic contact formed on the regrown n-GaN stripes when compared with conventional LEDs. Accordingly, the proposed approach simultaneously improves optical and electrical properties. In addition, strategies to further enhance the LEE up to the theoretical optimum value and control emission directionality are discussed. A way to overcome the low light extraction efficiencies of AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) has been shown. AlGaN-based DUV LEDs are promising DUV sources, but their light-extraction efficiency drops with decreasing wavelength because of their highly anisotropic light emission. Researchers in Korea and the United States demonstrate a strategy that exploits this characteristic. Specifically, they fabricated DUV LEDs that have light-emitting mesa stripes to efficiently extract DUV light from the AlGaN active region and reflectors between the stripes to reflect this light upward. This strategy simultaneously improves the optical and electrical properties of the DUV LEDs: they have both enhanced light output due a higher light-extraction efficiency and considerably lower operating voltages than conventional DUV LEDs. The researchers expect that the DUV LEDs can be further improved by optimizing their geometry.