Improved Light Extraction Efficiency of GaN-Based Ultraviolet Light-Emitting Diodes by Self-Assembled MgO Nanorod Arrays

Abstract

This paper presents using ultrasonic spray pyrolysis deposition method to grow MgO nanorod arrays on the top surface and the sidewall of the GaN-based ultraviolet light-emitting diodes. It is found that when the thickness of the MgO film is over 60 nm, the self-assembled MgO nanorod arrays are obtained. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, refractive index, extinction coefficient, and photoluminescence spectrum are used to analyze the structural, chemical, and optical characteristics of the MgO nanorod arrays. The LED chip with the MgO nanorod arrays shows slightly degraded electrical characteristics for it requires a higher forward voltage to provide 0.35-A forward current and higher series resistance. However, the LED chip with the MgO nanorod arrays has great improvement in electroluminescence and efficiency. Compared to the LED chip with a standard SiO2 passivation layer, the LED chip with the MgO nanorod arrays shows improvement of 14.1% in light output power (LOP), 12% in external quantum efficiency and wall plug efficiency. The uniformity of the LED performance like forward voltage, LOP, and wall-plug efficiency is investigated in this paper.