Materials Science & Engineering

“Transition Metal Oxides: New Opportunities for Electronics and Photonics”

Roman Engel-Herbert
Professor of Materials Science and Engineering
Pennsylvania State University

Transition metal oxides, although ubiquitous and highly functional, have barely made it into the application space of electronic and photonic devices. One major roadblock is their inferior material quality when synthesized in thin film form. While the structural perfection is high, evidenced by atomically abrupt interfaces, well defined heterostructures, and the demonstration of artificially layered oxide compounds grown with an impressive degree of control using physical vapor deposition techniques, such as pulsed laser deposition (PLD) or molecular beam epitaxy (MBE), the level of perfection needed to minimize unintentional extrinsic defect concentration to meet the stringent requirements for electronic and photonic devices has been found extremely challenging. In addition, the electronic functionality of transition metal oxides emerges from the d-orbitals, forming a narrow band with high carrier effective masses, marking an intrinsic limit to develop ever faster electronic devices based on this class of materials. Why then even bother about transition metal oxides?

In this talk I will discuss the application of an epitaxial thin film synthesis technique, dubbed hybrid molecular beam epitaxy, for the growth of transition metal oxide films in general and vanadium oxide and vanadate compounds in particular. This combinatorial approach of conventional MBE and chemical beam epitaxy (CBE) has been applied to the growth of SrVO3 and LaVO3, a correlated metal and a Mott insulator, as well as to the growth of high quality VO2 thin films. For all three cases the intrinsic material quality and its dependence on growth conditions will be discussed and compared to single crystal bulk standards. It will be shown that wafer scale growth of functional oxide thin films of ‘electronic grade’ quality is possible using this technique. The specific example of a transparent conductor is given to illustrate how transition metal oxides offer 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, are key to strike a new balance between the mutually exclusive demands of a high optical transparency and high electrical conductivity with metal-like carrier concentration. With a figure of merit comparable to the industry standard of the transparent conductor tin-doped indium oxide (ITO) at much thinner film thicknesses and lower cost of raw material the huge potential of this class of materials is exemplified for the application space of optoelectronics.



Dr. Engel-Herbert’s research is focused on the synthesis of oxide thin films targeted at developing novel artificial materials. Their properties are tailored through rational design achieved by arranging building blocks of condensed matter with atomic level precision. He has co-pioneered a novel thin film technique that enables the growth of complex oxides with an unprecedented level of perfection and has recently demonstrated that perovskite thin films can be integrated on Si using this scalable growth technique. He has made substantial contribution to the development of high-k dielectrics on compound semiconductors for beyond Si CMOS technology.

Honors and awards
• Rustum and Della Roy Innovation in Materials Award 2014.
• NSF Career Award 2014.
• Student’s Choice Faculty of the Year Award 2013.
• McFarlane Career Professorship, Department of Materials Science and Engineering, Pennsylvania State University, 2010-2013.
• Feodor-Lynen Award, Humboldt Foundation, 2008-2009.
• Carl Ramsauer Award, German Physical Society of Berlin, 2006.

322 ISE Lab
221 Academy Street
Newark, DE 19716

Hosting Organization:
Materials Science & Engineering
University of Delaware

March 2, 2016

10:30 a.m.