Nanocrystal-based Ohmic contacts on n and p-type germanium

摘要

We report a simple method of forming Ohmic contacts to n and p-type germanium (Ge) simultaneously using Au nanocrystals embedded in Ti contact metal. The electric field due to the work-function difference of Ti and Au reduces the tunneling resistance at the Ti-Au/Ge interface for n and p-type contacts. The nanocrystal-based contacts on n-Ge exhibit quasi-Ohmic current-voltage characteristics with >1000× increase in current density and an apparent reduction of 0.18 eV in the barrier height over Ti-Ge and Au-Ge contacts that show rectifying characteristics due to Fermi level pinning. On n+-Ge, the nanocrystal-based contacts exhibit Ohmic characteristics with >35× reduction in zero-bias resistance over Ti+-Ge contacts. Similar to Ti and Au contacts on p-Ge, Au nanocrystals embedded in Ti continue to exhibit Ohmic characteristics. This is in contrast to methods that convert p-type contacts from Ohmic to rectifying in the process of forming an Ohmic contact on n-Ge by inserting a thin dielectric layer between the metal and Ge. Device simulations reinforce the observed decrease in tunneling resistance due to the enhanced electric field at the Ti-Au/Ge interface.