Properties of GaN-based light-emitting diode thin film chips fabricated by laser lift-off and transferred to Cu

Conventional GaN-based light-emitting diodes (LEDs) on sapphire substrates and laser lift-off (LLO) lateral current structure GaN LED thin film chips on Cu substrates have been fabricated and their properties are compared. It is found that after the LLO process, the reverse bias leakage current obviously increases and equivalent parallel resistance decreases two orders accordingly. From analyses of I-V curves the fact that tunneling behavior dominates under the reverse bias is confirmed, and the LLO process aids more defects to become tunneling active whereas the similar ideality factors and equivalent series resistances of LLO-LEDs on Cu and conventional LEDs on sapphire suggest that the LLO process does not much damage the electrical characteristics at a forward bias. The analyses of L-I curves reveal that the LLO process induces more nonradiation centers. However, the LLO-LEDs show superior performance under large injection current. The LLO-LEDs have 1.8 times greater maximum output power and 2.5 times higher current operation capabilities than the conventional LEDs within 300 mA for the good thermal conductivity of Cu.