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

Abstract

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 3.4×10²⁰ cm⁻³ and surface Sn composition of more than 8%. This enables the realization of record-low specific contact resistivity ρc down to 4.4×10⁻¹⁰ Ω-cm². The average ρc 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-cm². This is also the lowest ρc 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 ρc as compared with a sample without segregation.