Au-free Si MOS compatible Ni/Ge/Al ohmic contacts to n⁺-InGaAs

Complementary metal-oxide semiconductor-compatible Ni/Ge/Al ohmic contacts to a n⁺-InGaAs layer exhibited a specific contact resistivity of 9.8 × 10^-8 Ωcm² at 300 and 5.1 × 10^-8 Ωcm² at 500 C. Only 7 nm of the n⁺-InGaAs layer was consumed during the Ni/Ge/Al ohmic formation. For comparison, Ni/Al and Ge/Ni/Al contacts showed a higher specific contact resistivity with significant consumption of the n⁺-InGaAs layer. The relatively low contact resistivities for Ni/Ge/Al are attributed to the transient increase in the donor concentration of n⁺-InGaAs. Ge metals segregated towards the n⁺-InGaAs surface and redistributed into the Ga and In sites, which increased the doping and acted as a diffusion barrier. These electrical and physical analyses of Ni/Ge/Al ohmic contacts to n⁺-InGaAs advance Au-free metallization techniques for highly scaled InGaAs channel metal-oxide field-effect transistors.