Optimization of surface morphology and electrical properties of Ti/Al/Ti–W/Au ohmic contacts to n-GaN by two-step annealing method

A two-step annealing method has been developed in order to optimize the electrical and morphological properties of Ti/Al/Ti–W/Au (20/100/40/100 nm) ohmic contacts on n-GaN. Using a one-step annealing process, the contact resistances exhibited by these multilayers were measured to be ranged from 0.29 ± 0.01 Ω mm at 750 °C for 60 s to 0.43 ± 0.01 Ω mm at 900 °C for 60 s. At the same time, the contact surface morphologies presented defects and showed surface roughnesses of around 80–120 nm. However, using the two-step annealing method, lower contact resistances, 0.25 ± 0.01 Ω mm, and an improvement of the contact surface morphology (surface roughness of 49 nm) were achieved after the optimization of the annealing parameters