1. Intellectual Merit: Graduate student Xuhui Luo and Prof. Alex Demkov at UT Austin have identified the source of the Fermi level pinning at the HfO2 surface. The so-called band bending resulting from this changes the apparent work function of the hafnia film, and has a profound effect on the band alignment with a metal, or in other words on the Schottky barrier height. In 1947 John Bardeen proposed a theory of rectification at a metal/semiconductor interface, which in contrast with the one originally proposed by Schottky [2] explained why the energy barrier an electron entering a semiconductor from the metal will see may be independent of the metal itself. In a nutshell, Bardeen proposed that charging of newly discovered surface states [3] caused the intrinsic band bending in the semiconductor. Performing first-principles calculations of thin oxide slabs Luo discovered that bands indeed bend as one goes from the bulk of the film to the surface. Below we show the boll and stick model of the surface of oxygen-terminated tetragonal hafnia, and a partial density of states projected onto p-states of oxygen one layer at a time. The state tracks the top of the valence band and the bending is quite obvious. This is a polar surface where the effect is most pronounced. Theoretical and Experimental Study of the Thermodynamic Stability of Amorphous Thin Films Based on Zirconia and Hafnia

2. J. Bardeen, Physical Review 71, 717 (1947). W. Schottky, Zeits. f. Physik 118, 539 (1942). Ig. Tamm, Physik. Zeits. Sowjetunion 1, 733 (1932). Theoretical and Experimental Study of the Thermodynamic Stability of Amorphous Thin Films Based on Zirconia and Hafnia

3. Broader Impact: This work has immediate applications in CMOS technology. Hafnia is succeeding silica as a gate dielectric in field effect transistors (the heart of every chip on the planet) and the biggest unresolved issue is the Fermi level pinning at the hafnia/metal interface. This result sheds light on the nature of the pinning. Another application is in surface catalysis on transition metal oxides where the position of the Fermi level defines frontier orbitals and thus chemical activity. Theoretical and Experimental Study of the Thermodynamic Stability of Amorphous Thin Films Based on Zirconia and Hafnia