Effect of Pd or Pt addition to Ti/Al ohmic contact materials for n-type AlGaN

Effects of Pd or Pt addition to Ti/Al ohmic contact materials used for n-type Al0.2Ga0.8N grown on the GaN substrates were studied where Si with 2×1018 cm−3 were doped in the AlGaN layers. The contact metals were prepared by depositing either by the electron-beam or thermal evaporation technique, and then annealed at high temperatures for 30 s in N2 atmosphere. It was found that the addition of a small amount of Pd or Pt to the Ti/Al ohmic contact materials reduced the contact resistivities of the Ti/Al contacts. The lowest contact resistivity of 4.1×10−6 Ω cm2 was obtained in the Ti(20 nm)/Pd(5 nm)/Al(200 nm) contact after annealing at 600 °C (where a slash “/” indicates the deposition sequence). The reduction of the contact resistivities by the Pd or Pt addition was believed to be due to increase in the donor concentration in the AlGaN layers by forming Pd–Ga or Pt–Ga compounds in the contact metals after annealing at elevated temperatures.