Awardee Interviews | Biography: Chris G. Van de Walle

Chris G. Van de Walle

Dr. Chris G. Van de Walle, University of California, Santa Barbara, “for seminal contributions to the theory of heterojunctions and its application to semiconductor technology, and for elucidating the role of hydrogen in electronic materials”

Chris Van de Walle obtained the degree of Engineer from the University of Gent, Belgium, in 1982, and a Ph.D. in Electrical Engineering from Stanford University in 1986. From 1986 to 1988 he was a postdoc at the IBM Watson Research Center in Yorktown Heights, New York. In 1988 he became a Senior Member of Research Staff at Philips Laboratories in Briarcliff Manor, New York, and in 1991 he joined the Xerox Palo Alto Research Center (PARC), becoming a Principal Scientist. Since 2004 he has been a Professor in the Materials Department at the University of California, Santa Barbara, and head of the Computational Materials Group.

Van de Walle’s research on heterojunctions started during his Ph.D. under the guidance of Richard Martin, Walter Harrison, and William Spicer. Working with Martin at PARC he carried out seminal calculations for Si/Ge interfaces, which have been widely used in the development of that materials system for high-speed electronics. He also developed a theory for heterojunction band offsets that continues to be employed for device modeling. During his postdoc under Sokrates Pantelides, Van de Walle started his first investigations of hydrogen in semiconductors. The excellent training offered by both Martin and Pantelides provided the foundation for Van de Walle’s application of first-principles calculations to a variety of technologically relevant materials topics throughout his career. He is also indebted to Eugene Haller, Matthias Scheffler, and Klaus Ploog for their mentorship and support.

At Philips, Van de Walle initiated research on wide-band-gap semiconductors, at first focusing on ZnSe. After joining PARC, he recognized the importance of GaN, performing comprehensive studies that debunked the myth that point  defects were responsible for n-type conductivity,
instead focusing attention on impurities as sources of unintentional doping. He also continued his research on hydrogen, elucidating the physics of hydrogenated amorphous silicon in collaboration with Robert Street, and performing in-depth studies of hydrogen in silicon with Noble Johnson and Conyers Herring. He had a series of excellent postdocs; the first of these, Jörg Neugebauer (now a Director at the Max Planck Institute in Düsseldorf), has continued to be a highly valued collaborator.

Van de Walle’s work expanded to address the interactions of hydrogen with many other semiconductors, for instance uncovering unexpected behavior as a shallow donor in ZnO. This culminated in the development (with Neugebauer) of the universal alignment model, which explains and predicts the electrical behavior of hydrogen in different materials by linking the electronic properties of hydrogen to the seemingly unrelated issue of band offsets. On an absolute energy scale, the electronic level of interstitial hydrogen was found to be constant across a wide range of semiconductors, insulators, and even aqueous solutions—the latter finding providing a link to electrochemistry.

At UCSB, Van de Walle has carried these research themes into new areas such as hydrogen storage materials and complex oxides. He strives to select research topics which combine high technological impact with a potential for elucidating new physics or materials science, and will continue to instill this research philosophy in his students and postdocs.