Ultra-low specific contact resistivity (1.4 × 10^-9 Ω·cm²) for metal contacts on in-situ Ga-doped Ge_0.95Sn_0.05 film

A heavily Ga-doped Ge_0.95Sn_0.05 layer was grown on the Ge (100) substrate by molecular beam epitaxy (MBE), achieving an active doping concentration of 1.6 × 10²⁰ cm^-3 without the use of ion implantation and high temperature annealing that could cause Sn precipitation or surface segregation. An advanced nano-scale transfer length method was used to extract the specific contact resistivity ρ_c between the metal and the heavily doped p-Ge_0.95Sn_0.05 layer. By incorporating Sn into Ge and in-situ Ga doping during the MBE growth, an ultra-low ρ_c of 1.4 × 10^-9Ω·cm² was achieved, which is 50% lower than the ρ_c of p⁺-Ge control and is also the lowest value obtained for metal/p-type semiconductor contacts.