Ab initio study of the electrostatic dipole modulation due to cation substitution in HfO2/SiO2 interfaces

The interface between HfO2 and SiO2 is of much technological interest for complementary metal-oxide semiconductor (CMOS) technology in microelectronic devices. The valence band offset between HfO2 and SiO2 is a property of particular importance for this interface because it can be modulated by adding substitutional cations like Al, La, and Mg. We study the effects of these substitutional cations within this interface by using ab initio techniques in order to obtain the electrostatic dipole modulation and the corresponding change in the valence band offset in relation to dopant free reference HfO2/SiO2 interfaces. Al, La, and Mg are substituted for both Hf and Si atoms close to the interface during a detailed analysis of the dipole at the microscopic scale. This reproduces not only the experimental trends, but also demonstrates that the effects of the dopants are strongly dependent upon their positions and their chemical environments. Specifically, the modulation of the charge distribution by the dopants shows a complicated structure consisting of several peaks that contribute to the interfacial dipole centered around the oxygen atoms that bridge between the HfO2 and the SiO2. We also include a first-order G(0)W(0) correction to recover band offset results compatible with the experimental values.