Efficiency boosting of 236 nm AlGaN-based micro-LEDs

Abstract

In this study, 236 nm AlGaN-based deep ultraviolet (DUV) Micro-LEDs with different sized P-contact areas are designed and fabricated, and the sidewall is restored by wet chemical treatment method with KOH solution. The results reveal that proper KOH treatment could effectively remove plasma damaged materials and clearly show the formation of m-plane facets. Compared with untreated Micro-LEDs, the reverse leakage current of the treated Micro-LEDs under -10 V decreases by up to 91.7% and the specific contact resistivity reduces from 6.94 Ωcm2 to 0.07 Ωcm2. The underlying mechanism is that KOH treatment removes the sidewall defects which leads to surface nonradiative recombination sites and surface leakage. Moreover, KOH treatment also removes contaminations on the P+-GaN surface and leads to lower specific contact resistivity. However, too long treatment also destructs the 20 nm P+-GaN layer, which results in higher voltage but less DUV light absorption. As a result, peak light output power density increases from 2.12 W/cm2 to 4.01 W/cm2, representing an 89.2% increase. The efficiency enhancement of Micro-LEDs is anticipated to facilitate the development of DUV Micro-LEDs in maskless lithography and high-capacity DUV non-line of sight communication.