Low resistance and reflective Mg-doped indium oxide-Ag ohmic contacts for flip-chip light-emitting diodes

We have investigated an Mg-doped In_xO_y(MIO)-Ag scheme for the formation of high-quality ohmic contacts to p-type GaN for flip-chip light-emitting diodes (LEDs). The as-deposited sample shows nonlinear current-voltage (I--V) characteristics. However, annealing the contacts at temperatures of 330°C-530°C for 1 min in air ambient results in linear I--V behaviors, producing specific contact resistances of 10^-4--10^-5 Ω·cm². In addition, blue LEDs fabricated with the MIO-Ag contact layers give forward-bias voltages of 3.13-3.15 V at an injection current of 20 mA. It is further shown that LEDs made with the MIO-Ag contact layers give higher output power compared with that with the Ag contact layer. This result strongly indicates that the MIO-Ag can be a promising scheme for the realization of high brightness LEDs for solid-state lighting application.