Journal
APPLIED PHYSICS LETTERS
Volume 93, Issue 20, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3028343
Keywords
alumina; cobalt; current density; elemental semiconductors; Fermi level; germanium; iron; MOSFET; nickel; ohmic contacts; oxidation; rectification; Schottky barriers; semiconductor-metal boundaries; tunnelling; valence bands; work function
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Funding
- Western Institute of Nanoelectronics (WIN)
- Intel Spin-Gain FET project.
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Due to the strong Fermi-level pinning close to the germanium (Ge) valence band edge, all metal/p-type Ge contacts show Ohmic characteristics, while metal/n-type Ge contacts exhibit rectifying behaviors. In this paper, we report a simple method to alleviate this Fermi-level pinning effect by inserting a thin layer of aluminum oxide (Al2O3), formed by oxidation of aluminum (Al), between the metal/Ge interface. The effective Schottky barrier heights of nickel (Ni)/n-type Ge, cobalt (Co)/n-type Ge, and iron (Fe)/n-type Ge decrease from 0.54, 0.62, and 0.61 eV to 0.39, 0.23, and 0.18 eV, respectively, with this thin layer of Al2O3. The tunneling oxide significantly suppresses the Fermi-level pinning, and yet does not restrict the current density. This method seems promising to realize low resistance metal contact to n-type Ge, which is essential to realize n-channel Ge complementary metal-oxide-semiconductor field-effect transistor with metal source and drain.
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