Ferroelectric Si-doped HfO2 thin films are integrated into three different device stacks with a p+ Ge substrate, a p+ Si substrate, and a TaN bottom metal gate. The ferroelectric behavior of the Si-doped HfO2 thin films are strongly dependent on the bottom interfaces. Si-doped HfO2 thin films have favorably improved ferroelectric properties on the p+ Ge substrate due to the lack of a dielectric interfacial layer between HfO2 and Ge. The low voltage operation and cycling stability of Si-doped HfO2 ferroelectric thin films on Ge can lead to the realization of high performance, robust Ge ferroelectric field effect transistors for nonvolatile memory applications.