Comparison of Ohmic contact resistances of n- and p-type Ge source/drain and their impact on transport characteristics of Ge metal oxide semiconductor field effect transistors

Abstract

We report the results of a systematic study to understand low drive current of Ge-nMOSFET (metal–oxide–semiconductor field-effect transistor). The poor electron transport property is primarily attributed to the low dopant activation efficiency and high contact resistance. Results are supported by analyzing source/drain Ohmic metal contacts to n-type Ge using the transmission line method. Ni contacts to Ge nMOSFETs exhibit specific contact resistances of 10 − 3 –10 − 5 Ω cm 2, which is significantly higher than the 10 − 7 –10 − 8 Ω cm 2 of Ni contacts to Ge pMOSFETs. The high resistance of Ni Ohmic contacts to n-type Ge is attributed mainly to insufficient dopant activation in Ge (or high sheet resistance) and a high tunneling barrier. Results obtained in this work identify one of the root causes of the lower than expected Ge nMOSFET transport issue, advancing high mobility Ge channel technology.