Abstract：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 $W_{\rm fin}$, and inversion charge density $N_{\rm inv}$. With the fixed $W_{\rm fin}$, fin directions of $\langle 110\rangle$, $\langle 1\bar{1}2\rangle$ and $\langle \bar{1}10\rangle$ within (001), (110), and (111)-oriented wafers provide the maximum values of electron mobility. The optimized $W_{\rm fin}$ for mobility is also dependent on wafer orientation and channel direction. As $N_{\rm inv}$ increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as $N_{\rm inv}$ increases.
2019, Vol. 36 
