Investigation of Cr- and Al-based metals for the reflector and Ohmic contact on n-GaN in GaN flip-chip light-emitting diodes

This letter investigates three composite metals used as a reflector and Ohmic contact on n-GaN to simplify the process in a flip-chip light-emitting diode (FCLED). The investigated composite metals were TiAlTiAu, CrAlCrAu, and CrTiAu. The specific contact resistivities of the TiAlTiAu, CrAlCrAu, and CrTiAu Ohmic contacts on n-GaN were changed from 1.4× 10-4, 1.7× 10-4, and 1.9× 10-4 cm2 to 1.3× 10-4, 1.1× 10-4, and 3.3× 10-5 cm2, respectively, after 500 h of thermal stress. The corresponding operating voltages of FCLEDs with different composite metals were changed by less than 1%. After 96 h of thermal stress, the luminous intensities of the three structures decreased by 6.2%, 11.1%, and 1.4%, respectively. The GaN FCLED that was fabricated with CrTiAu as a reflector and an Ohmic contact on n-GaN exhibits good thermal stability and luminous intensity.