Al2O3 Passivation Layer for InGaN/GaN LED Deposited by Ultrasonic Spray Pyrolysis

This letter utilizes ultrasonic spray pyrolysis (USP) to deposit Al₂O₃ as the passivation layer of GaN light-emitting diodes (LEDs). The composition of Al₂O₃ is analyzed by X-ray photoelectron spectroscopy. The refractive index and transmittance of USP-grown Al₂O₃ are investigated. The thickness of Al₂O₃ is determined to be 70 nm, which is close to the optimum from antireflection theorem calculation for the wavelength of 455 nm. The coverage quality and thickness are confirmed by transmission electron microscopy. The light output power (LOP) of USP-grown-Al₂O₃-passivated InGaN/GaN LED is improved from 321 mW to 347 mW compared with an LED without passivation. The forward voltage (V_F) and series resistance (R_s) are not subject to significant variations but the shunt resistance (R_SH) is increased after Al₂O₃ passivation. LED chips with Al₂O₃ and SiO₂ passivation are packaged as LED lamps. Devices passivated by USP-grown Al₂O₃ show slightly better LOP performance than those passivated by plasma-enhanced chemical vapor deposition-grown SiO₂.