Scaled layers of HfO 2 on LaGeO x on Ge grown by molecular beam deposition and their electrical properties and passivation are discussed. The interfacial LaGeO x thickness as well as the deposition temperature of the HfO 2 cap are varied and the effects thereof on properties like peak mobility and interface trap distributions are compared. We report on negative threshold voltages, around -0.8 V, in combination with scaled devices with a minimum EOT of 1.4 nm, which shows beneficial characteristics for the LaGeO x passivation of Ge. The effect of various post-metallization anneals in FG and O 2 is shown to improve the gate stack properties of the scaled samples, yielding higher peak mobilities with maximum values of about 120 cm 2/Vs for annealed samples. The impact of LaGeO x interfacial layer thickness and HfO 2 deposition temperature on the density of interface traps (Dit) distributions for as-deposited and annealed samples is discussed, and Hf in-diffusion into the LaGeO x is shown to be detrimental to its passivation of Ge. The Dit distributions are measured by the full conductance technique on MOSFETs at room temperature as well as 233 K and are then correlated with the mobilities extracted from the same devices. © 2011 American Institute of Physics.