Vertical Structure GaN-Based Light Emitting Diodes with Electrochemically Deposited Stress-Free Nickel Substrate

Abstract

Ni substrates were electrochemically deposited on p-GaN side of vertical structure GaN-based light emitting diodes (LEDs). The Ni substrate functions as a part of p-electrode, a heat sink, and a mechanical supporter of vertical structure LED devices. Using a proper Ni electrodeposition bath, the residual stress of 50-μm thick Ni substrates was lower than 10 MPa, which is very low to be regarded as stress-free. Stress-free Ni substrate with better mechanical strength than Cu substrate was effective in minimizing mechanical damage possibly generated during LED chip fabrication. Vertical structure LED devices comprised in a 2-inch Ni-supported wafer had forward voltage on average as low as 3.35 V at 20 mA compared with 3.54 V of Cu-supported LED devices. Ni-supported LED devices showed comparable optical performance to Cu-supported LED devices in output power and operation reliability at constant forward currents. Electrical and optical performances of vertical structure LEDs with WO 3 -added Cu substrate, which was previously considered to enhance the mechanical property of pure Cu substrate, were also presented for reference. In conclusion, Ni substrate affects the efficiency of vertical structure LEDs positively more than Cu and WO 3 -added Cu substrates as long as those substrates are electrodeposited equally in stress-free conditions.