  The phosphorous activation in Ge n$^{+}$/p junctions is compared in terms of
junction depth, by using laser spike annealing at 860{\deg}C for 400$\mu$s. The
reverse junction leakage is found to strongly depend on the abruptness of
dopant profiles. A shallow and abrupt junction is shown to have lower
phosphorous activation level, due to surface dose loss, and higher band-to-band
tunneling (BTBT) leakage, when compared to the deep junction. Simulations were
carried out to evaluate the lowest achievable OFF-state currents (I$_{OFF}$)
for Ge double-gate FETs when using such an abrupt junction. Our results
indicate that a Ge body thickness smaller than 5 nm is required to suppress the
BTBT leakage and meet the requirement for the high performance devices defined
by the International Technology Roadmap for Semiconductors (I$_{OFF}$ =
10$^{-7}$ A/$\mu$m).
