Optical Spectroscopy of Carbon Nanotube p-n Junction Diodes Ji Ung - PowerPoint PPT Presentation

Optical Spectroscopy of Carbon Nanotube p-n Junction Diodes Ji Ung Lee College of Nanoscale Science and Engineering University at Albany-SUNY p n 6 th US-Korea Forum on Nanotechnology April 28-29, 2009 jlee1@uamail.albany.edu 1

The College of Nanoscale Science & Engineering and The College of Nanoscale Science & Engineering and Albany NanoTech Complex at the University at Albany Albany NanoTech Complex at the University at Albany jlee1@uamail.albany.edu 2

State-of-the-Art Infrastructure NanoFab 300N NanoFab 300S $50M, 150K ft 2 $175M, 228K ft 2 32K Cleanroom 60K Cleanroom Completed: 03/04 Completion: 10/08 NanoFab 200 NanoFab 300E $100M, 250K ft 2 $16.5M, 70K ft 2 Completion: 1Q/09 4K Cleanroom Completed: 06/97 750K ft 2 cutting-edge facilities (96,000 ft 2 300mm Wafer Cleanrooms). $4.5B investments and 2500 R&D jobs on site. jlee1@uamail.albany.edu 3

300 mm Wafer Processing Capability ANT/CNSE will house over 125 state-of-the-art 300mm wafer tools when build out is completed. Designed for 32nm node & beyond but compatible with previous generations. • Unit process, module integration, and full flow capability. • Facility will have a 45nm baseline process for use by partners. Facility capable of 25 integrated wafer starts (WSD) per day. • 24/7 operation, wafer release 6 Days / Week jlee1@uamail.albany.edu 4

Device fabrication on 300mm wafers >1000 devices/die ~100 nm features Advanced processes 70nm 70nm jlee1@uamail.albany.edu 5

Why study the p-n diode: • The p-n junction diode is the most fundamental of all the semiconductor devices – it is the basis for the majority of solid state devices. • For fundamental understanding of semiconductors: Example: Hall-Shockley-Read Theory. For any new semiconductor, a proper characterization of the p-n diode is important. jlee1@uamail.albany.edu 6

Interplay between transport and optical properties: • SWNT Diode Fabrication and DC Characteristics • Optical Properties: Photovoltaic Effect Enhanced Optical Absorption - Excitons • Origin of the Ideal Diode Behavior (BGR-Bandgap Shrinkage) jlee1@uamail.albany.edu 7

Bulk p-n junction diode basics: I V N-type(electrons) P-type(holes) Diode Equation: (ideal if n=1) E C Equilibrium I=I o (e qV/nKT -1) E F E V I E C Forward Bias (Recombination) E V 2 V E C Reverse Bias 3 1 (Generation) E V jlee1@uamail.albany.edu 8

Electrostatic doping: p n Carrier Concentration Split gates VG1,2 J.U. Lee et. al., APL: July 5, 2004 jlee1@uamail.albany.edu 9

S D 2 gate device 20µm VG1 VG2 3 and 4 gate devices jlee1@uamail.albany.edu 10

CNT diode/rectifier: (p-n or n-p diode devices) 1 10 -6 p S D -10V -10V 5 10 -7 0 10 0 -5 10 -7 n p p n S D S D +10V -10V -10V +10V -1 10 -6 -1.5 -1 -0.5 0 0.5 1 1.5 V DS (Volts) J.U. Lee et. al., APL: July 5, 2004 jlee1@uamail.albany.edu 11

Nearly Ideal Diode Characteristics with n~1 (1.2) 10 -7 p n 10 -8 p 10 -9 qV = − nK T I I ( e 1 ) n B o 10 -10 VGS1,2=+/-10V Fit 10 -11 -0.4 -0.2 0 0.2 0.4 V DS (Volts) jlee1@uamail.albany.edu 12

Series Resistance Limits Current: 10 -7 R s Rs: 10 -8 measured from the resistive 10 -9 mode – due to n-type to metal 10 -10 contact resistance. 10 -11 -0.4 -0.2 0 0.2 0.4 V DS (Volts) jlee1@uamail.albany.edu 13

Suspended SWNT Diodes: (a) (b) p n 1 µm Suspended tube formed based on a self-registering technique jlee1@uamail.albany.edu 14

Ideal Diodes with Ideality Factor n=1.0 for Suspended Diodes -7 10 1.E-07 1.E-08 -8 1.E-09 10 1.E-10 1.E-11 Fit Data -9 1.E-12 10 1.E-13 IDS (Amps) -0.5 0 0.5 -10 10 R s n=1.0 SWNTs are -11 10 perfect, substrates are not. -12 10 -13 10 -0.5 0 0.5 1 V DS (V) J.U. Lee, Appl. Phys. Lett. 87, 073101 (2005) jlee1@uamail.albany.edu 15

Photovoltaic Effect 8x10 -12 ( λ =1.5 µm) n p 4x10 -12 LED Voc and Isc: IDS (Amps) Completely define PV properties for an 0 ideal diode Voc PV -4x10 -12 Isc PD Increase Intensity -12 -8x10 -0.2 -0.1 0 0.1 V DS (V) J.U. Lee, Appl. Phys. Lett. 87, 073101 (2005) jlee1@uamail.albany.edu 16

Exciton Peaks in the Photocurrent Spectra (similar to SWNTs in solution) -11 10 -12 10 IDS (A) -13 -14 10 4x10 3 1 -14 10 -15 -14 10 3x10 -0.10 -0.05 0.00 0.05 0.10 VDS(V) 2 4 I SC (A) -14 2x10 5 3 -14 1x10 1 0 0.5 1.0 1.5 Energy (eV) J.U. Lee et.al., Appl. Phys. Lett. 90, 053103 (2007) jlee1@uamail.albany.edu 17

DOS: One Electron Model DOS: One Electron Model D. O. S. D. O. S. D. O. S. D. O. S. E E E E 3D 2D 1D 0D Bulk Semiconductor Quantum Well Quantum Wire Quantum Dot jlee1@uamail.albany.edu 18

EXCITONS IN CARBON NANOTUBES continuum Exciton Hydrogenic Levels n=1,2,3… Electron-Hole Coulomb Interaction e 2 H eh = − ε| r e − r h | results in the electron-hole binding that forms the exciton states below the conduction subband edge jlee1@uamail.albany.edu 19

Sommerfeld Factor: Coulomb Interaction Excitons 3D: Absorption Coulomb Effects E Energy 2D: Absorption Coulomb Effects Energy 1D: Absorption Coulomb Effects Energy jlee1@uamail.albany.edu 20

Sommerfeld Factor in 1D -> 0 at Eg T. Ogawa and T. Takaghara, Phys. Rev. B 43, 14325 (1991) jlee1@uamail.albany.edu 21

Spectra with similar first energies 1 = E11 3 = E22 2.0 E B 2 I SC (Normalized) 1.5 Lack of any features at Eg due to 1.0 Sommerfeld factor <1 0.5 Side bands measure dark 0.6 0.8 1.0 1.2 1.4 exciton Energy (eV) J.U. Lee et.al., Appl. Phys. Lett. 90, 053103 (2007) jlee1@uamail.albany.edu 22

Comparison to Photoluminescent Data: 2.0 +: Emperical Kataura Intensity (a.u.) Weisman et.al. Nano Lett. 3, 1235 (2003) 1.6 - E 11 and E 22 – Exciton-phonon Energy (eV) ▲ - Quasipaticle Bandgap 100 200 300 -1 ) Raman frequency (cm 1.2 Continuum: 1.55eV/nm 0.8 E11: 1.01eV/nm 0.4 1.0 1.2 1.4 1.6 1.8 2.0 E B : 0.54 eV/nm Diameter (nm) jlee1@uamail.albany.edu 23

Origin of the Ideal Diode Behavior and Exciton Dissociation: -8 10 Ideal Diodes: -9 10 n=1.0 1.0 -10 40 10 3 = E22 1 = E11 30 -11 0.9 10 2 IDS (A) 4 I SC (fA) 20 5 = E33 -12 10 0.8 10 -13 10 E 11 (eV) 0 0.5 1.0 1.5 -14 10 Energy (eV) 0.7 E 11 =E a -15 10 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.6 VDS (V) Two mechanism for n=1.0: 0.5 0.4 0.5 0.6 1) Direct Band-to-Band E a (eV) 2) Diffusion of Minority Carriers Ea < E11 ?? from the doped regions jlee1@uamail.albany.edu 24

Many-Body Renormalization of Band structure (BGR – band gap renormalization) and Proposed Mechanism for Exciton Dissociation: L n p I sc n E B E a E C D S 2 E F E 11 1 p 3 E V E a I sc p n Formation of heterointerfaces along a homogenous material J.U. Lee, Phys. Rev. B 75, 075409 (2007) jlee1@uamail.albany.edu 25

Device Ideal for Studying BGR: Variable Doping with VG1,2: 1E-8 6V • Diode follows n p 1E-9 8V 11V ideal relation with 1E-10 S D doping. SiO 2 1E-11 IDS (A) VG1 VG2 1E-12 • Evidence of L strong BGR: Io 1E-13 when Doping . 1E-14 w/o BGR Io when 1E-15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 Doping . VDS (V) jlee1@uamail.albany.edu 26

Origin of increase in Io with Doping: No Shrinkage Minority Increase shrinkage of the Carriers of the Doping band gap band gap E f E f E f P type w/o BGR: w/ BGR: semiconductor minority carrier minority decreases carrier increases! jlee1@uamail.albany.edu 27

Conclusions: • Bipolar devices are more fun to study. • How do neutral excitons dissociate to generate large photocurrents? • Window to the study of many-body effects: BGR, biexctions, etc… Funding: NSF, NRI/INDEX, IFC, IBM and UAlbany jlee1@uamail.albany.edu 28

Future Work: Graphene p-n junctions: Optics-like manipulation of electrons n- n- -type -type type type p- p- -type -type type type n n p p 1,2...layer 1,2...layer graphene graphene flake flake Split Gates Split Gates jlee1@uamail.albany.edu 29