Metal/P-type GeSn Contacts with Specific Contact Resistivity down to 4.4×10−10 Ω-cm2

Ga and Sn surface-segregated p
⁺
-GeSn (Seg. p
⁺
-GeSn) was grown by molecular beam epitaxy (MBE) to achieve an average active Ga doping concentration of 3.4×10
²⁰
cm
^-3
and surface Sn composition of more than 8%. This enables the realization of record-low specific contact resistivity ρ
_c
down to 4.4×10
^-10
Ω-cm
²
. The average ρ
_c
extracted from 14 sets of Ti/Seg. p
⁺
-GeSn Nano-TLM test structures, a collection of more than 90 devices is 6.5×10
^-10
Ω-cm
²
. This is also the lowest ρ
_c
for non-laser-annealed contacts. Ti contacts to p
⁺
-GeSn films with and without Ga and Sn surface segregation were fabricated. It is shown that the segregation of Ga and Sn at the Ti/p
⁺
-GeSn interface leads to 50% reduction in ρ
_c
as compared with a sample without segregation.