Effects of Thermal Annealing on V‐Based Ohmic Contacts on n‐Type AlGaN with High Al Content

The effects of thermal annealing on V‐based electrodes (V/Al/X/Au) with different diffusion barrier metal X are investigated for n‐type Al 0.7 Ga 0.3 N. At an annealing temperature of 800 °C, linear current ( I )–voltage ( V ) characteristics are obtained, and the specific contact resistivities of the electrodes for X = Pt, Ni and V are 9.7 × 10 −5 , 2.3 × 10 −4 , and 1.8 × 10 −4 Ω cm 2 , respectively. When the annealing temperature is increased to 850 °C, the I–V characteristics become nonlinear. Especially in the case of the V diffusion barrier, significant degradation of the ohmic contact is observed. The coverage of the electrode on the n‐type Al 0.7 Ga 0.3 N surface is significantly reduced after thermal annealing at 850 °C, resulting in a decrease in the current value. Furthermore, the formation of V–Al–Au and Al–Au alloys and diffusion of Au to the interface between the n‐type Al 0.7 Ga 0.3 N and electrode are found. The Au diffusion preferentially occurs through the domain boundaries of the alloys and causes the deterioration of the ohmic contact properties. In contrast, from the viewpoint of miscibility, Pt and Ni diffusion barriers are more effective than V in suppressing the formation of alloys with Au and then the diffusion of Au.