The energy band alignment between Ge, HfO 2 and Al 2 O 3 was analyzed as influenced by passivating interlayers (ILs) of different composition (GeO 2 , Ge 3 N 4 , Si/SiO x ). From internal photoemission and photoconductivity experiments we found no IL-sensitive dipoles at the Ge/HfO 2 interfaces, the latter being universally characterized by conduction and valence band offsets of 2.1 and 3.0eV, respectively. However, in the case of HfO 2 growth using H 2 O-based atomic layer deposition, the Ge oxide IL appears to have a narrower bandgap, 4.3eV, than the 5.4–5.9eV gap of bulk germania. Accordingly, formation of this IL yields significantly reduced barriers for hole and, particularly, electron injection from Ge into the insulator. Changing to a H-free process for HfO 2 and Al 2 O 3 deposition suppresses the formation of the narrow-gap Ge oxide.