We succeeded in improving a TiN/Ge contact by optimizing the TiN deposition. From contact resistance measurements of TiN/n+-Ge, the specific contact resistivity was determined to be 7.9×10-6 Ω·cm2 for a surface impurity concentration of 3.9×1019 cm-3, suggesting that an interlayer between TiN and Ge is conductive. It was also found that a peripheral surface-state current dominated the reverse leakage current of the contact. The leakage current was significantly decreased by the surface passivation using GeO2. The passivated TiN/p-Ge contact showed a high hole barrier height of 0.57 eV, implying an extremely low electron barrier height of 0.09 eV.

Metal/Ge contacts with high Schottky barrier heights on p- and n-Ge substrates could be formed using direct sputter depositions from TiN and Hf, respectively. The barrier heights were 0.53 and 0.60 eV for the p- and n-Ge substrates, respectively, which are available to source/drains (S/Ds) in Schottky n- and p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs). We fabricated the n- and p-MOSFETs and demonstrated their operation. In particular, the n-MOSFET operation is the first demonstration of S/D using directly contacted metal/Ge. This work opens a method for embodying Schottky S/D Ge complementary MOS devices.

No abstract