Theoretical investigation of metal/n-Ge1−xSnx (0 ≤ x < 0.11) contacts using transfer matrix method

The carrier transmission properties and the specific contact resistivity for metal/n-Ge1−xSnx contacts with various Sn compositions ranging from 0% to 11% are modelled by the transfer matrix method. It is found that increasing the Sn composition enhances the electron tunneling between metal and Γ valley and lowers the ρc by more than 4 times when the donor concentration (NA) is below 1 × 1020 cm−3; when NA is higher than this, electron tunneling from the L valley dominates and ρc is insensitive to change in the Sn composition. The impact of contact metals on ρc for metal/n-Ge0.89Sn0.11 contacts is also investigated. Metals with a lower effective mass are preferred when NA is below 2 × 1020 cm−3, while for a higher NA, a metal with a higher effective mass is preferred to further lower ρc. This is due to the transition from Γ valley-dominant tunneling to L valley-dominant tunneling with increasing NA.