Experimental Extraction of Ballisticity in Germanium Nanowire nMOSFETs

In this paper, we report the experimental extraction of ballistic transport parameters of high-performance Germanium Nanowire nMOSFETs (Ge NWTs) with lengths ${L}_{\text {NW}} = {40}$ –100 nm, width ${W}_{\text {NW}} = {40}$ nm, and height ${H}_{\text {NW}} = {10}$ nm using temperature-dependent measurements. The extracted contact resistivity ( $\rho {c}$ ) and sheet resistance (Rsh) imply that parasitic series resistance ( ${R}_{\text {SD}}$ ) of fabricated Ge NWTs is affected by $\rho _{c}$ of the metal-nGe ( ${3.42} \times {10}^{-{5}}\,\,\Omega \cdot \text {cm}^{{2}}$ at 292 K), which decreases with the increase in temperature. Ballistic efficiency (BE) is found to be 22%–47% at 292 K depending on the dimension of the device. It decreases with increased temperature and increases with ${L}_{\text {NW}}$ scaling down to 40 nm. The transition region with fluctuating BE is observed near ${L}_{\text {NW}} = {50}$ –60 nm, where the electron transport enters deeper into bthe allistic regime. BE is found to be sensitive to temperature and drops from 58% (170 K) to 37% (390 K) for ${L}_{\text {NW}} = {40}$ -nm Ge NWT. Therefore, in order to maintain the high ballisticity of the devices, it is important to optimize the device structure and eliminate the self-heating effect.