High-Performance Ge nMOSFETs With $\hbox {n}^{+}\hbox {-} \hbox {p}$ Junctions Formed by “Spin-On Dopant”

We report high-mobility Ge nMOSFETs using a simple approach to form n⁺-p junctions by rapid thermal diffusion of "spin-on dopant" to avoid implantation damage. These junctions show a high I_ON/I_OFF ratio (~10⁵ -10⁶) and an ideality factor of ~1.03, indicating a low defect density in the junction, whereas ion-implanted junctions show higher /off (by approximately one to two orders) and a larger ideality factor (n ~ 1.45). Germanium (100) nMOSFETs with diffusion doping and GeO₂ passivation show a high I_ON/I_OFF ratio of ~10⁴-10⁵, a low SS of 111 mV/decade, and a high μ_eff (679 cm² · V^-1 · s^-1 at peak). The diffusion-doped devices also show lower (approxi mately one order) GIDL and a higher (~1.3×) drive current of ~12 μA/μm in an L ~ 20 μm device at V_G - V_T = 2 V and V_D = 1 V, compared to the implanted devices. Moreover, diffusion-doped Ge (111) devices show even higher μ_eff (970 cm² · V^-1 · s^-1 at peak) and ~1.5× enhancement over the diffusion doped Ge (100) devices and surpass the universal Si mobility at low effective fields.