First-principles exploration of alternative gate dielectrics: Electronic structure of ${\mathrm{ZrO}}_2/\mathrm{Si}$ and ${\mathrm{ZrSiO}}_4/\mathrm{Si}$ interfaces

We employed first principles simulations using density functional theory within the local density approximation to investigate the electronic properties of the ${\mathrm{ZrO}}_2/\mathrm{Si}$ and ${\mathrm{ZrSiO}}_4/\mathrm{Si}$ interfaces. We considered the interfaces between the (001) surfaces of tetragonal zirconia $(t-{\mathrm{ZrO}}_2)$ or zircon $\left({\mathrm{ZrSiO}}_4\right)$ and a silicon (100) substrate. We find that ${\mathrm{ZrO}}_2/\mathrm{Si}$ interfaces exhibit partial occupation of zirconium dangling bonds (Zr $d$ states) at the Fermi level when the zirconium coordination is reduced from its bulk coordination. Hydrogen passivation of zirconium atoms, as well as oxygen bridging at the interface, can remove the partial occupancy of $d$ orbitals at the Fermi level. The calculated band offsets of these interfaces show asymmetric band alignments, with conduction band offsets between 0.64 and 1.02 eV and valence band offsets between 3.51 and 3.89 eV, depending on the zirconium and oxygen coordination at various ${\mathrm{ZrO}}_2/\mathrm{Si}$ interfaces. By contrast, the ${\mathrm{ZrSiO}}_4/\mathrm{Si}$ interface shows no partial occupation of zirconium dangling bonds at the Fermi level and provides a more symmetric band alignment, with a much higher conduction band offset of 2.10 eV and a valence band offset of 2.78 eV. These results suggest that ${\mathrm{ZrSiO}}_4$ may form an excellent interface with silicon in terms of its electronic properties and therefore may be a suitable candidate for replacing ${\mathrm{SiO}}_2$ as a gate insulator in silicon-based field effect transistors. On the other hand, we suggest that ${\mathrm{ZrO}}_2$ will require additional interface preparation or postdeposition annealing to yield adequate electronic properties for gate dielectric applications.