Improved Light Output Power of InGaN/GaN LED by Using Ultrasonic Spray Pyrolysis Deposited MgO

This paper presents an MgO thin films deposited by an ultrasonic spray pyrolysis deposition method to serve as passivation and antireflection layers of the InGaN/GaN light-emitting diodes (LEDs). The electrical, electroluminescence (EL), and efficiency characteristics of the LEDs with 60-, 70-, and 80-nm MgO films are investigated. It is found that the LEDs with the MgO films have lower reverse currents and higher shunt resistance than that without an MgO film. However, there are no significant differences of the forward voltage at 350 mA and the series resistance between the LEDs with and without the MgO films. The significant differences between the LEDs with and without the MgO films are the light output power (LOP) and efficiency. The LED with 70-nm MgO film has the highest LOP of 556 mW (at 700 mA) and external quantum efficiency of 40.8% (at 30 mA). Further, the LED chips with the MgO films show better LOP and wall plug efficiency than those with the SiO2 and SiNx films. It is also found that the LED chips with MgO film as a passivation layer shows stable electrical and EL characteristics in the aging time test.