High-Performance Ge nMOSFETs With 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 ION/IOFF 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 ION/IOFF ratio of ~104-105, a low SS of 111 mV/decade, and a high μeff (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 VG - VT = 2 V and VD = 1 V, compared to the implanted devices. Moreover, diffusion-doped Ge (111) devices show even higher μeff (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.