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Isaac Childres and Yong P. Chen Department of Physics, Birck Nanotechnology Center,

Graphene FET for Radiation Sensing and Rad-hard Electronics. Isaac Childres and Yong P. Chen Department of Physics, Birck Nanotechnology Center, and School of Electrical & Computer Engineering Purdue University, West Lafayette IN http://www.physics.purdue.edu/quantum

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Isaac Childres and Yong P. Chen Department of Physics, Birck Nanotechnology Center,

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  1. Graphene FET for Radiation Sensing and Rad-hard Electronics Isaac Childres and Yong P. Chen Department of Physics, Birck Nanotechnology Center, and School of Electrical & Computer Engineering Purdue University, West Lafayette IN http://www.physics.purdue.edu/quantum Contact: ichildre@purdue.edu, yongchen@purdue.edu, (765) 494-0947 1/11/2013 Argonne National Laboratories Instrumentation Frontier Community Meeting Session J:  Emerging Technologies, 10:45am-12pm

  2. Outline • Brief Intro: graphene field effect transistors (GFET) • Radiation detection with GFET (on undoped substrates) • epitaxial GFET on SiC • - response to X-ray, gamma-rays & visible light @ room T • exfoliated GFET on undoped Si • CVD graphene on CdTe, GaAs, … • Radiation hardness of GFET (on doped Si/SiO2) • - suspended graphene (no substrate) promising for rad-hard • (tested with e-beam irradiation) • Summary Acknowledgments My group members: Dr. Ozhan Koybasi (now @ Harvard) Gabe Lopez (now @ Sandia), Dr. Amol Patil (now @ Canberra), Dr. Romaneh Jalilian (now @ NaugaNeedles), Collaborators: Prof. Igor Jovanovic, Mike Foxe and Edward Cazalas (Purdue & Penn State Nuclear Engineering)

  3. Graphene field effect transistor (GFET) Usual solid graphene (doped Si) “Dirac” point (DP)/“Charge-neutral” point (CNP) DOS graphene Usual 2DES Insulator (300nm SiO2) semiconductor Vgate Vgate E DOS graphene p-type(holes) n-type(electrons) E [Electric field] Unique Electronic Properties of Graphene (2D electron system) • Ways to make graphene: • exfoliation from graphite (small) • epitaxial growth on SiC (large) • chemical vapor deposition (large) • Exceptional Electronic Properties • High conductivity/mobility (>10X Si @ room T) • Low (electronic) noise • Ultra-sensitivity • Tunable (electr.) properties • Flexible, transparent and low-cost IBM’09

  4. “Dirac pt” (<n>=0) n p graphene insulator semiconductor Vgate Vgate Sharp Electric Field Effect in Graphene FET (doped) Finite R(quantum R) Low noise High mobility (ballistic) High speed (THz) High sensitivity (dE/E<10-3) Bandgap engineering possible … all these even at 300K “the sharp feature” with low electrical noise (even @ room T) [Electric field] F. Schedin et al’2007 R~0.1 for ~1 electrons induced/depleted in graphene – superb charge sensor! (room T) R. Jalilian et al., Nanotechnology 22, 295705 (2011)

  5. Graphene as • built-in room-T • low-noise pre-amp, • and it is: • light • transparent • flexible • low-cost Gamma (MCNP-CASINO) • Graphene a highly sensitive to detect local E-field change: “sharp” feature • NOT relying on collecting ionized charges; appearance of ionized charges changes electric field • can work with variety of absorber substrates best suited: gamma/neutron interaction; room-T (wide bandgap); energy resolution (narrow bandgap) - less stringent requirement on substrate mobility etc. • low noise (even at room T), graphene (semimetal) resistance stays finite unlike MOSTFET channel Principle of Radiation Detection:Using Graphene Field Effect Transistors on undoped substrates I I V V graphene E=V/d strong E-field Vgate Vgate semiconductor ionized weak E-field back gate irradiation Graphene resistance DR M. Foxe et al. IEEE Trans. Nanotech. 11, 581 (2012)

  6. Experimental Facilities @ Purdue for in-situ Testing of GFET Device Response to Radiation (exfoliated)graphene probe GFET Device (top view) 5 μm 200 μm Mini X-ray source (~10-40keV;107-108/cm2s@wafer) shield 2.75 in Probe Station GFET on Undoped Substr. Variable T (4-400K) probe station 4He dewar Type of radiation tested: X-rays; gamma ray (rad source); light

  7. Bandgap Si 1.1 eV SiC 3.2 eV Epitaxial Graphene grown on SiC Sublimation of SiC Berger et al.’06 HRL Courtesy Profs. Mike Capano & Peide Ye (Purdue ECE & Birck Nanotechnology Center) D TG GFET on SiC (undoped) S 10um

  8. X-ray response of GFET on SiC (doped Si) graphene semiconductor Vgate Vgate T = 300 K R (k) SiC (undoped) graphene is n-type (doped by SiC) VGate (V) A. Patil et al. IEEE NSS’10’11; A. Patil et al. submission (2013)

  9. X-ray response of GFET on SiC VG=20V VG=40V On Off VG=0V VG=-50V Off R (k) Device:G5D6 VGate (V) A. Patil et al. IEEE NSS’10’11; A. Patil et al. submission (2013)

  10. Response dependence on X-ray flux or energy • Increasing flux and/or energy •  increasing ionized regions • increasing change of E • field •  more response! Increase flux  X-ray spectrum Ileak (nA) Increase (av.) energy 

  11. (doped Si) graphene semiconductor Vgate Vgate GFET on SiC: Gamma response Cs-137 ( source) 11mCi  SiC (undoped) Back gate V Device 1 Device 2

  12. (doped Si) graphene semiconductor Vgate Vgate GFET on SiC: light response Epitaxial graphene on undoped SiC response to broad range of radiation (X-ray, -ray, light) @ room T! SiC (undoped) vary intensity O.Koybasi et al, SPIE Proc’12

  13. low flux (15kV,15µA) high flux (40kV,80µA) T=4.3K “undoped” Si wafer starts to freezes out No response at VG=0: Response is due to field effect! substrate is (almost) insulating substrate is conductive X-ray source: VX=40 kV, IX= 60 μA GFET VG=20V Substrate: “undoped” Si 4.3K 300K X-ray off X-ray on (40kV,80μA) GFET on undoped Si: Response to X-ray Radiation exfoliatedgraphene i-Si • Radiation (X-ray) response demonstrated • in GFET on (undoped) Si [T <~150K] ! • Need larger bandgap substrate for room T operation!

  14. Large-scale Graphene Grown by Chemical Vapor Deposition Graphene-on-demand: Grown by CVD on Cu foil then transfer to arbitrary substrates! • Wide bandgap substrates (SiC, CZT etc.): room T/high T operation • Narrow bandgap substrates (InSb): high energy resolution H. Cao et al., Appl. Phys. Lett. (2010); W. Wu et al., Sensors & Actuators B (2010) also Ruoff (Austin); Hong (SKKU/Samsung) etc… CVD furnace @ Purdue-QMD Lab SiO2/Si glass Si GaAs CdTe 14

  15. CVD Graphene on CdTe: X-ray response X-ray response at various X-ray source voltage (energy) on off Substrate: undoped CdTe X-ray response observed at room T Ozhan Koybasi’ 12

  16. graphene insulator semiconductor absorber Vgate Ultimate Sensitivity: single (gamma) photon detection possible! x107 2.1 Sharp field effect curve Even single gamma cause sufficient E-field change! M. Foxe & G. Lopez et al., Proc. IEEE NSS 2009 IEEE Trans. Nanotech, 11, 581 (2012) 1.1 Ionized/conducting region

  17. h+ e- h+ e- graphene SiO2 Silicon (doped) Vgate Vgate Part 2: Test rad-hardness of GFET with electron-beam • shift (-) VDP n-dope graphene • reduce conductivity/mobility defects Supported on SiO2/Si Suspended graphene Conductance (ohm-1) 30keV electron beam I= 0.15nA; Expose area: 50um x 50um Exposure time  dosage Suspended Suspended graphene (no substrate): much smaller shift! -- good for rad-hard electronics?! I. Childres et al. Appl. Phys. Lett. (2010) I. Childres et al. SPIE proceeding (2011) • High energy electrons ionize e-h pairs in Si wafer • Less mobile holes trapped at oxide-Si interface, inducing electrons in the channel (graphene) • Analogous to the well-known negative-shift of threshold voltage in MOSFET subject to high energy ionizing irradiation

  18. Summary • Graphene field effect transistors (GFET): sensitive to charge & E-field! • Radiation detection with GFET (on undoped substrates) • epitaxial GFET on SiC • - response to X-ray, gamma-rays & visible light @ room T • exfoliated GFET on undoped Si • CVD graphene on CdTe, GaAs, … • Radiation hardness of GFET • -suspended graphene (no substrate) promising for rad-hard • (tested with e-beam irradiation) Ongoing Work/Future Directions Sensitivity: single  Neutron detection Speed Energy resolution Graphene+BN etc Funnel/drain charges multiplexing New collaborations started with ANL HEP group (applications of GFET) & Purdue’s Bortoletto group (proton radiation hardness and effect on GFET)

  19. Reverse Bias improves response speed (relaxation time) Light Response of GFETs with CVD Graphene on SiC Light on Ozhan Koybasi et al. ‘12 Detector operated at a gate bias voltage of +50V. When light is turned off, the gate bias is very quickly changed to -50V or -100V and then back to +50V

  20. Scanning Gate Microscopy & Charge Sensitivity Contact Mode SGM 100 nm Ag2Ga nanowire parylene 5 mm R. Jalilian et al., Nanotechnology 22, 295705 (2011) • Charge inhomogeneity due to local extrinsic doping: • metal contacts induced doping (n for Ti/Au we used) • edge of graphene (p in air) • residues/adsorbates… large charge (e-h) puddles near Dirac “neutral” point! SGM images of charge inhomogeneity R~0.1 for ~1 electrons induced/depleted in graphene – superb charge sensor! (room T)

  21. Graphene for radiation detection Urgent Need: New Radiation Detection w/t (Nano)Technologies Radiation detection in low flux applications “The gravest danger we face---nuclear terrorism…” --- 07/16/08 at Purdue University (Summit on Confronting New Threats) “And the biggest threat that we face right now is not a nuclear missile coming over the skies. It's in a suitcase.” --- 09/28/2008 during 1st Presidential debate • Current state-of-art detectors can not • meet the need (cost/sensitivity…)! • High-Purity Ge (gamma ray) • Superconductor trans. edge sensor (gamma) • 3He (neutron) Graphene-based Ultrasensitive Advanced Radiation Detectors also: X-ray/gamma-ray astronomy/dark matter

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