Bonding and interface states of Si:HfO2 and Si:ZrO2 interfaces

First principles calculations of the (100)Si:ZrO2 and HfO2 interfaces are presented. A number of interface configurations satisfying valence bonding requirements are constructed, and their total energies, relaxed structures, interface electronic states and band offsets are calculated. An interface with three coordinated oxygen sites is found to be the most stable oxygen-terminated interface for a 1x1 surface unit cell, and an interface with a tenfold coordinated Hf is the most stable for the metal-terminated interfaces. All the oxygen-terminated interfaces satisfying the valence requirements are found to be semiconducting, without gap states. The tenfold coordinated metal-terminated interface is found to be metallic, making this interface not useful for devices. The band offsets are found to vary by up to 0.7 eV for different interface terminations, showing that band offsets can in principle be controlled by chemistry.