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Properties of Suspended ZnO Nanowire Field-Effect Transistor

Properties of Suspended ZnO Nanowire Field-Effect Transistor. Scott Cromar Mentor: Jia Grace Lu University of California, Irvine 31 August 2006. Wide & direct bandgap semiconductor (E g =3.35 eV) Field effect transistors (FETs) Gas & chemical sensing Optoelectronics & Micro-lasers.

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Properties of Suspended ZnO Nanowire Field-Effect Transistor

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  1. Properties of Suspended ZnO Nanowire Field-Effect Transistor Scott Cromar Mentor: Jia Grace Lu University of California, Irvine 31 August 2006

  2. Wide & direct bandgap semiconductor (Eg=3.35 eV) Field effect transistors (FETs) Gas & chemical sensing Optoelectronics & Micro-lasers NW Synthesis Suspended ZnO NW FET fabrication Electrical contact improvement techniques Sensing experiment results Next step ZnO Nanowires (NWs) Advantages Objectives Fan, Z.; Lu, J.G. "Zinc Oxide Nanostructures: Synthesis and Properties." Journal of Nanoscience and Nanotechnology 5 (2005): 1561-1573.

  3. Nanowire Synthesis O2 O2 Catalyst Zn Au catalyst ZnO nanowire Vapor Trapping Chemical Vapor Deposition (CVD) • Absorbs Zn • Vapor • Au-Zn Alloy • Supersaturation • Nucleation • 1D Crystal Structure • ZnO Nanowire • Au Catalyst • 700 °C Chang, P.-C.; Fan, Z.; Wang, D.; Tseng, W.-T.; Chiou, W. -A.; Hong, J.; Lu, J. G. “ZnO nanowires synthesized by vapor trapping CVD method.” Chem. Mater. 16 (2004): 5133-5137

  4. Nanowire Synthesis Furnace Diameter = 30-100 nm O2 Gas Flow Zn Vapor Zn Powder Quartz Vial Quartz Tube Si Chip

  5. Nanowire Synthesis

  6. Sonicate NW chip in isopropanol Drop solution on pattern, Ti/Au contact Search for device w/ optical microscope ZnO NW FET Fabrication

  7. ZnO NW FET Fabrication Nanowire (Channel) Source Drain Gate Ti/Au SiO2 Vds P++Si Vg

  8. ZnO NW FET Fabrication

  9. Annealing 300 - 700 °C, 30 min. Metal deposition w/ Focused Ion Beam Improve Contact

  10. Gas Sensing Depletion Region NW Channel Source Drain Gate • NWs have high surface-volume ratio • Suspended NW have more surface area than nonsuspended • Gas molecules on metal-oxide surface alter the electronic properties by chemisorption Fan, Z.; Lu, J. G. “Chemical sensing with ZnO nanowire field-effect transistor.” IEEE Transactions on Nanotechnology 5 (2006): 393-396.

  11. Gas Sensing Results • Sensitivity: • Nonsuspended: 90% • Suspended: 10% I-Vds curve for various concentrations of NO2 Conductance of NW exposed to 1000 ppm CO2 Ggas= Transconductance on gas exposure G0 = Trasconductance in inert environment

  12. Next Step • Further investigate the intrinsic properties of suspended ZnO NWs • More gas sensing • Gating characteristics • Mechanical & electrical properties w/ SPM • Identify device applications

  13. Acknowledgements • Professor Jia Grace Lu • CJ Chien • Joseph Fan • IM-SURE staff • Carl Zeiss Inc. (SEM use) • Funding through NSF

  14. Scanning Probe Microscopy (SPM) Scanning Surface Potential Microscopy (SSPM) Surface Potential Results F = electrostatic force dC/dz = derivative of the tip-sample capacitance Vac = magnitude signal applied tip Vtip – Vsample = potential difference between tip and sample Fan, Z.; Lu, J. G. “Electrical properties of ZnO nanowire field effect transistors characterized with scanning probes.” Applied Physics Letters 86 (2005): 032111.

  15. Surface Potential Results Surface Topology Surface Potential

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