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

• Published in: Applied physics letters Vol. 101; no. 18
• Main Authors: Paramahans Manik, Prashanth, Kesh Mishra, Ravi, Pavan Kishore, V., Ray, Prasenjit, Nainani, Aneesh, Huang, Yi-Chiau, Abraham, Mathew C., Ganguly, Udayan, Lodha, Saurabh
• Format: Journal Article
• Language: English
• Published: 29-10-2012
• Subjects: Barriers; Conduction band; Current density; Electrical resistivity; Germanium; Thin films; Titanium; Zinc oxide
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4764909

We report low resistance Ohmic contacts on n-Ge using a thin ZnO interfacial layer (IL) capped with Ti. A 350°C post metallization anneal is used to create oxygen vacancies that dope ZnO heavily n-type (n+). Rectifying Ti/n-Ge contacts become Ohmic with 1000× higher reverse current density after insertion of n+-ZnO IL. Specific resistivity of ∼1.4×10−7 Ω cm2 is demonstrated on epitaxial n+-Ge (2.5×1019 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.