title: Vertical nanowire heterojunction devices based on a clean Si/Ge interface.
abstract: Different vertical nanowire heterojunction devices were fabricated and tested based on vertical Ge nanowires grown epitaxially at low temperatures on (111) Si substrates with a sharp and clean Si/Ge interface. The nearly ideal Si/Ge heterojuctions with controlled and abrupt doping profiles were verified through material analysis and electrical characterizations. In the nSi/pGe heterojunction diode, an ideality factor of 1.16, subpicoampere reverse saturation current, and rectifying ratio of 10(6) were obtained, while the n+Si/p+Ge structure leads to Esaki tunnel diodes with a high peak tunneling current of 4.57 kA/cm(2) and negative differential resistance at room temperature. The large valence band discontinuity between the Ge and Si in the nanowire heterojunctions was further verified in the p+Si/pGe structure, which shows a rectifying behavior instead of an Ohmic contact and raises an important issue in making Ohmic contacts to heterogeneously integrated materials. A raised Si/Ge structure was further developed using a self-aligned etch process, allowing greater freedom in device design for applications such as the tunneling field-effect transistor (TFET). All measurement data can be well-explained and fitted with theoretical models with known bulk properties, suggesting that the Si/Ge nanowire system offers a very clean heterojunction interface with low defect density, and holds great potential as a platform for future high-density and high-performance electronics.
authors.affiliation: Department of Electrical Engineering and Computer Science, The University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.forename: Wayne Y
authors.initials: WY
authors.lastname: Fung
authors.forename: Wei
authors.initials: W
authors.lastname: Lu
mesh_terms: D003460:Crystallization; D005857:Germanium / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D053770:Nanowires / Q000737:chemistry*; D010316:Particle Size; D012825:Silicon / Q000737:chemistry*
chemical_list: D005857:Germanium; D012825:Silicon