Phonon Limited Electron Mobility in Germanium FinFETs: Fin Direction Dependence**Supported by the National Natural Science Foundation of China under Grant Nos 61534004, 61604112 and 61622405.

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We investigate the phonon limited electron mobility in germanium (Ge) fin field-effect transistors (FinFETs) with fin rotating within (001), (110), and (111)-oriented wafers. The coupled Schrödinger–Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas, and Fermi’s golden rule is used to calculate the phonon scattering rate. It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge FinFETs. The phonon limited electron motilities are influenced by wafer orientation, channel direction, fin thickness Wfin, and inversion charge density Ninv. With the fixed Wfin, fin directions of , and within (001), (110), and (111)-oriented wafers provide the maximum values of electron mobility. The optimized Wfin for mobility is also dependent on wafer orientation and channel direction. As Ninv increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as Ninv increases.