One-Dimensional Transport in Nanowire Heterostructures

Two-dimensional (2D) electron and hole gas systems have been a major platform for basic research in condensed-matter physics, as well as high performance electrical and optical devices. In this talk, I will discuss a one-dimensional (1D) hole gas system based on a germanium/silicon core/shell nanowire heterostructure. At room temperature, hole accumulation in the intrinsic germanium channel was observed due to the valence band offset at the Ge/Si interface. At low temperatures, conductance quantization at values close to that expected of a ballistic conductor was observed, and was attributed to the long mean free path in the hole gas and confinement of the hole gas in the radial direction. These effects showed little temperature dependence and suggested that transport in these small diameter nanowires is ballistic even at room temperature. Field-effect transistors made from these nanowires exhibited on current and transconductance among the highest reported in nanostructures, with a 100 percent device yield. The demonstration of a 1D hole gas in a flexible nanowire heterostructure opens up a number of possibilities for investigating quantum phenomena in 1D systems, as well as applications in nanoelectronics. Other nanowire heterostructures such as nonvolatile memories and metallic interconnects will also be discussed.
Wei Lu was born in Xinxiang, Henan, China, in 1973. He received the B.S. degree in physics with minor in electrical and computer engineering from Tsinghua University, Beijing, China, in 1996, and the M.A. and Ph.D. in physics from Rice University, Houston, TX in 1999 and 2003, respectively. Since 2003, he has been a postdoctoral research fellow at the Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA. His current research is on electrical transport in one-dimensional nanowires, and developing nanowire based devices, including field-effect transistors and non-volatile memories. His Ph.D. work includes low-temperature transport studies on single-electron transistors and quantum dots, and radio-frequency time domain studies on electron tunneling phenomena. From 1996 to 2003, he was a Research and Teaching Assistant in the Department of Physics, Rice University. Dr. Lu was the recipient of the Chuoke Award in 1997 and 1998, and Wilson Award in 2003.