(Invited) The Effects of Zinc-Tin-Oxide Nanosphere Monolayer on Improvement of Light Extraction in Light-Emitting Diodes

Abstract

Over the last two decades, III-nitride-based light-emitting diodes (LEDs) have been widely used for our daily life, such as illumination, various backlight units for full-color displays, and automotive headlamps. In spite of the versatile advantages of GaN-LEDs, relatively low external quantum efficiency is still a problem to expand their application fields. For the viable solution to unravel pending issues in solid state light-emitting research fields, many efforts have been conducted. In this study, we report on the applications of zinc-tin-oxide (ZTO) nanoparticles and monolayer as a light extraction layer for GaN-based LEDs. The ZTO layers formed on top of an LED epi-structure with a variable Sn-ratio, which was deposited by the spin coating method. The transmission spectra of the ZTO layers with Zn to Sn ratios of 1:1 (ZTO-I) and 1:5 (ZTO-II) exhibited optical transmittances of 98% and 88% in the visible region, respectively. The electroluminescence (EL) and light power-current-voltage (L-I-V) measurements show that double ZTO layers consisting of various Zn to Sn ratios led to enhanced light extraction from blue LEDs. Finally, we will discuss the effects of ZTO monolayer transferred onto the p-GaN surface on the external quantum efficiency of LEDs. The ZTO monolayers were prepared by using the ZTO nanospheres synthesized by precipitation solution method. The transferred ZTO nanosphere monolayers on top surface of LED are very effective way to improve the light extraction efficiency.