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Hafnium dioxide has been recently introduced as a gate dielectric in the field effect transistors. It belongs to a class of high dielectric constant or high-k dielectrics. We briefly discuss the structural and electronic properties of bulk hafnia, and show how oxygen vacancies believed to affect the band alignment across the metal oxide semiconductor (MOS) stack are stabilized in hafnia films next to high work function metals.

Continuous scaling in semiconductor technology, associatsed with Moore’s law, brought new materials in every functional element of Si-based metal-oxide-semiconductor (MOS) field effect transistors (FET). In particular, for a gate dielectric instead of traditional SiO2 new HfO2-based oxides with higher dielectric constants are now used. The introduction of these so-called high-k dielectrics opened the possibility of using high mobility semiconductors instead of Si in MOS technology. In this chapter we discuss density functional calculations of high-k oxides hafnia and zironia. After briefly describing theoretical methods used in our calculations we discuss the bulk properties, surfaces and interfaces of hafnia and zirconia relevant to advanced gate stack engineering.

We use a combination of density functional theory and calorimetric measurements to investigate the monoclinic to tetragonal transition in hafnia and zirconia. We measure the transition enthalpies to be $8.4\ifmmode\pm\else\textpm\fi{}0.7\text{ }\text{kJ}/\text{mol}$ in hafnia and, as previously reported, $5.272\ifmmode\pm\else\textpm\fi{}0.544\text{ }\text{kJ}/\text{mol}$ in zirconia. Calculated values are 10.21 and 7.50 kJ/mol for hafnia and zirconia, respectively. We formulate a theoretical model of the phase transition consistent with the martnesitic character of the transformations. The transition barriers of 20.3 and 16.3 kJ/mol are estimated for hafnia and zirconia, respectively. We report the phonon spectra of monoclinic and tetragonal phases of both oxides and identify the Raman and IR active modes. The theoretical results compare well with available experiments. We present a comprehensive theoretical comparison of thermodynamic properties of zirconia and hafnia including the temperature dependence of specific heat.

Hafnium dioxide that belongs to a class of metal oxides with a high dielectric constant or high-k dielectrics has been recently introduced as a gate dielectric in field effect transistors. We report a theoretical study of structural and electronic properties of hafnia surface, and the electronic structure and band alignment at hafnia interfaces with metals, oxides and semiconductors that are crucial in gate stack engineering.

We present a joint experimental and theoretical study of ultrathin hafnia films grown on Si (001) by atomic layer deposition for applications as a gate dielectric of a field-effect transistor. The structural analysis by means of high-resolution transmission electron microscopy, electron diffraction, and x-ray diffractometry indicates films with thickness of 4 nm or less to be polycrystalline, predominantly monoclinic and textured, with the texture axis being the normal to the $(21\overline{1})$, $(11\overline{2})$, and their equivalent planes. Films with thickness around 10 nm consist of a mixture of monoclinic and tetragonal phases more or less randomly oriented. Films thicker than 25 nm are purely monoclinic with $(\overline{1}11)$ and (111) textures. Using density-functional theory we investigate surface energies of monoclinic and tetragonal hafnia films in search for thermodynamic means of controlling the film microstructure. We report the atomic and electronic structures of these films including the surface energy, work function, and electron affinity.

We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO2. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.