Semiconductor heterostructures are central for all modern electronic and optoelectronic devices. Traditional semiconductor heterostructures are typically created through a "chemical integration" approach with covalent bonds, and generally limited to the materials with highly similar lattice symmetry and lattice constants (and thus similar electronic structures) due to lattice/processing compatibility requirement. Materials with substantially different structure or lattice parameters can hardly be epitaxially grown together without generating too much defects that could seriously alter their electronic properties. In contrast, van der Waals integration, where pre-formed materials are "physically assembled" together through van der Waals interactions, offers an alternative "low-energy" material integration approach (vs. the more aggressive "chemical integration" strategy). The flexible "physical assembly" approach is not limited to materials that have similar lattice structures or require similar synthetic conditions. It can thus open up vast possibilities for damage-free integration of highly distinct materials beyond the traditional limits posed by lattice matching or process compatibility requirements, as exemplified by the recent blossom in van der Waals integration of a broad range of 2D heterostructures. Here I will discuss van der Waals integration as a general material integration approach beyond 2D materials for creating diverse heterostructures (e.g., dielectric/semiconductor and metal/semiconductor) with minimum integration-induced damage and interface states, enabling high-performing devices (including high speed transistors, diodes, plasmonic devices) difficult to achieve with conventional "chemical integration" approach. A particular highlight is the creation of van der Waals metal/semiconductor contacts free of interfacial disorder and Fermi level pinning, thus for the first time enabling experimental validation of the Schottky-Mott rule first proposed in 1930s.
Dr. Duan received his B.S. Degree from University of Science and Technology of China in 1997, and Ph.D. degree from Harvard University in 2002. He was a Founding Scientist and then Manager of Advanced Technology at Nanosys Inc., a nanotechnology startup founded based partly on his doctoral research. Dr. Duan joined UCLA with a Howard Reiss Career Development Chair in 2008, and was promoted to Associate Professor in 2012 and Full Professor in 2013. Dr. Duan's research interest includes nanoscale materials, devices and their applications in future electronic, energy and health technologies. Dr. Duan has published over 200 papers with over 40,000 citations, and holds over 40 issued US patents. For his pioneer research in nanoscale science and technology, Dr. Duan has received many awards, including MIT Technology Review Top-100 Innovator Award, NIH Director's New Innovator Award, NSF Career Award, Alpha Chi Sigma Glen T. Seaborg Award, Herbert Newby McCoy Research Award, US Presidential Early Career Award for Scientists and Engineers (PECASE), ONR Young Investigator Award, DOE Early Career Scientist Award, Human Frontier Science Program Young Investigator Award, Dupont Young Professor, Journal of Materials Chemistry Lectureship, International Union of Materials Research Society and Singapore Materials Research Society Young Researcher Award, the Beilby Medal and Prize, the Nano Korea Award, and most recently International Society of Electrochemistry Zhao-Wu Tian Prize for Energy Electrochemistry.