Untying a Gordian Knot in Oxide Thin Film Growth
Roman Engel-Herbert, PhD
Associate Professor of Materials Science and Engineering and Physics
Department of Materials Science and Engineering, Penn State University
Despite being ubiquitous and highly functional, oxide materials containing transition metal elements have barely made it into the application space of electronic and photonic devices. One major roadblock is their inferior material quality compared to bulk single crystals when synthesized in thin film form. The growth of phase pure material with high structural perfection has been found a formidable but solvable task and atomically abrupt interfaces, well defined heterostructures, and artificially layered oxide compounds have been successfully grown by physical vapor deposition techniques. However, achieving a level of material perfection where unintentional point defect concentrations are low enough to meet the stringent requirements demanded by electronic and photonic application has been found extremely challenging.
In this talk I will discuss recent progress made to overcome this challenge. In an attempt to disentangle the Gordian Knot that seems to tie lack of stoichiometric control and thin film synthesis together, a combinatorial approach of physical and chemical vapor deposition techniques has been applied to the growth of complex oxide thin films. Taking the correlated metal SrVO3 as an example, thin film quality and its dependence on growth conditions will be discussed and compared to single crystal bulk standards. It will be shown that functional oxide thin films of ‘electronic grade’ quality are possible. The improved control over the film’s stoichiometry due to the superior growth kinetics at play is a mandatory requirement to study the intrinsic properties of transition metal oxide thin films, whose electronic properties are dominated by the d orbitals. The specific example of a transparent conductor is given to illustrate how this class of materials offers new design strategies beyond conventional semiconductors with band structures derived from s and p orbitals. It will be shown that the high carrier effective mass, originating from the small band width of the conduction band derived from d orbitals and a sizeable electron electron interaction, are key to strike a new balance between the mutually exclusive demands of a high optical transparency and high electrical conductivity beyond the conventional paradigm.
