Fermi-level unpinning and low resistivity in contacts to n-type Ge with a thin ZnO interfacial layer

摘要

We report low resistance Ohmic contacts on n-Ge using a thin ZnO interfacial layer (IL) capped with Ti. A 350 ℃ post metallization anneal is used to create oxygen vacancies that dope ZnO heavily n-type (n~+). Rectifying Ti-Ge contacts become Ohmic with 1000× higher reverse current density after insertion of n~+-ZnO IL. Specific resistivity of ～ 1.4 × 10~(-7) Ωm~2 is demonstrated on epitaxial n~+-Ge (2.5 × 10~(19) cm~(-3)) layers. Low resistance with ZnO IL can be attributed to (a) low barrier height from Fermi-level unpinning, (b) good conduction band alignment between ZnO and Ge, and (c) thin tunneling barrier due to the n~+ doping.