The reliability of Hf0.5Zr0.5O2 (HZO) metal-ferroelectric-semiconductor capacitors grown by plasma-assisted atomic oxygen deposition on Ge substrates is investigated with an emphasis on the influence of crystallization annealing. The capacitors show very weak wake-up and imprint effects, allowing reliable operation in excess of 10 years, which is attributed partly to the clean, oxide-free Ge/HZO bottom interface. The weak temperature dependence and the observed asymmetries between polarization up and down states and between positive and negative coercive voltage shifts lead to the conclusion that imprint is controlled by carrier injection at the top electrode interface. The latter mechanism is associated with trapping at interfacial oxygen-vacancy defects. On the other hand, using ultrafast (millisecond) flash annealing improves the leakage current by at least an order of magnitude and the endurance by a factor of 3 compared to conventional rapid thermal annealing, which makes them suitable for low power nonvolatile memory applications where (ultra)thin HZO is an essential requirement.