ZnO: an attractive option for n-type metal-interfacial layer-semiconductor (Si, Ge, SiC) contacts

We propose ZnO as an attractive interfacial layer (IL) option for n-type metal-IL-semiconductor (MIS) contacts because of (i) good conduction band alignment between ZnO and Si/Ge/SiC, (ii) high n-type doping possible in ZnO, and, (iii) low Fermi-level pinning factor for metal/ZnO contacts. Device simulations suggest better scalability for MIS contacts versus silicides/germanides for future FinFET technologies. Contact diode measurements on Ti/n⁺-ZnO/n-Ge and Ti/n⁺-ZnO/n-Si devices show nearly 1000X increase in current densities due to the presence of an n⁺-ZnO IL. In comparison to alternate IL options such as Al₂O₃ and TiO₂, n⁺-ZnO gives significantly higher current densities on n-Ge as demonstrated through device simulations and experimental data. Specific contact resistivity of (0.8-1.5) × 10^-6 Ω cm² is demonstrated through four-probe measurements on circular TLM devices fabricated on n⁺-Ge (1 × 10¹⁹ cm^-3) epi layers using n⁺-ZnO IL.