Ohmic contact formation of Ti/Al/Ni/Au to n-GaN by two-step annealing method

摘要

The thermal annealing effects on Ti/Al/Ni/Au Ohmic contact to n-GaN are investigated by current-voltage (Ⅰ-Ⅴ) characteristics and transmission line method (TLM) measurements. The cladding layer of Ni/Au on Ti/Al plays two roles: preventing inter-diffusion of Ti, Al, Au and anti-oxidation of the contacting layer. The specific contact resistance (ρ_c) of Ti/Al/Ni/Au to n-GaN increases slightly at first with the increasing annealing temperature (T_a). When T_a increases above 500℃, ρ_c decreases monotonously in the range of 400-900℃. However, the morphology of the contact degrades gradually when T_a increases above 600℃. The minimum of ρ_c is obtained as 9.65 x 10~(-7) Ωcm~2 by two-step annealing method in this work. Finally, the roles of two-step annealing method in the formation mechanism of the Ohmic contact to n-GaN are also discussed.