title: Dopant-free GaN/AlN/AlGaN radial nanowire heterostructures as high electron mobility transistors.
abstract: We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire heterostructures and their implementation as high electron mobility transistors (HEMTs). The radial nanowire heterostructures were prepared by sequential shell growth immediately following nanowire elongation using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/AlN/AlGaN radial nanowire heterostructures are dislocation-free single crystals. In addition, the thicknesses and compositions of the individual AlN and AlGaN shells were unambiguously identified using cross-sectional high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM). Transport measurements carried out on GaN/AlN/AlGaN and GaN nanowires prepared using similar conditions demonstrate the existence of electron gas in the undoped GaN/AlN/AlGaN nanowire heterostructures and also yield an intrinsic electron mobility of 3100 cm(2)/Vs and 21,000 cm(2)/Vs at room temperature and 5 K, respectively, for the heterostructure. Field-effect transistors fabricated with ZrO(2) dielectrics and metal top gates showed excellent gate coupling with near ideal subthreshold slopes of 68 mV/dec, an on/off current ratio of 10(7), and scaled on-current and transconductance values of 500 mA/mm and 420 mS/mm. The ability to control synthetically the electronic properties of nanowires using band structure design in III-nitride radial nanowire heterostructures opens up new opportunities for nanoelectronics and provides a new platform to study the physics of low-dimensional electron gases.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Yat
authors.initials: Y
authors.lastname: Li
authors.forename: Jie
authors.initials: J
authors.lastname: Xiang
authors.forename: Fang
authors.initials: F
authors.lastname: Qian
authors.forename: Silvija
authors.initials: S
authors.lastname: Gradecak
authors.forename: Yue
authors.initials: Y
authors.lastname: Wu
authors.forename: Hao
authors.initials: H
authors.lastname: Yan
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Blom
authors.forename: Charles M
authors.initials: CM
authors.lastname: Lieber
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry*; D004583:Electrons; D005708:Gallium / Q000737:chemistry*; D046911:Macromolecular Substances; D046529:Microscopy, Electron, Transmission; D049329:Nanostructures; D014173:Transistors, Electronic
chemical_list: D017607:Aluminum Compounds; D046911:Macromolecular Substances; C513700:aluminum gallium nitride; C473348:gallium nitride; C052045:aluminum nitride; D005708:Gallium