Charge transport in organic semiconductors and organic field effect transistors Andrej Golubkov IF – Seminar, Graz,

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Co-Workers  Egbert Zojer  Peter Pacher  Harald Etschmaier

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Outline  Part I: Charge transport models –Comparison to inorganic semiconductors –Drude model –Hopping transport models  Part II: Building and analyzing FETs –Building process –temperature dependend Measurements  Part III: Parameter extraction and first results –Parameter extraction –Mobility vs. temperature

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Charge carrier transport models. Part I: overview based on reviews from Gilles Horowitz

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Comparison (Molecular) Crystal Covalent Metallic Gilles Horowitz

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Conjugated organic materials  sp2 hybridization of carbon  3 σ bonds from (2s, 2p x, 2p y )‏  1 π bond from 2p z

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Simple band transport: Drude model  free moving carriers, acceleration by external field  scattering at phonons, impurieties

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs  Temperature dependence of v th  Temperature dependence of scattering process: mean free path between phonons, charged impurities Simple band transport: Drude model W. Warta

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Polaron transport  Polarization by one single charge  dressed (by π- electros) charge residence time el. polarization time bandwidth bandgap Gilles Horowitz

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Polaron transport Gilles Horowitz Silinish E.A, Capek V.

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Polaron transport Silinish E.A, Capek V. Eg Charge modulated spectroscopy Peter J. Brown

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Hopping (polaron) Transport  useful for disordered materials (polymers)‏  Bässler's model –transport by hopping between localized states –(Polarisation) Energy of the states fluctuates –DOS is described by gausian distribution of variance σ –charge transport: random walk energy difference intersite distance

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Hopping (polaron) Transport  Perculation theory by Vissenberg & Matters –Variable range hopping among exponential DOS –Conduction through 'resistor network': infinite cluster with the highest conductivity is relevant –Gate voltage (charge density) dependence

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Hopping (polaron) Transport Pentacene 300 K180 K117 K A. R. Brown

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Multiple trapping & thermal release  Assumptions –carriers arriving at trap -> capture –release is thermaly activated –2 sorts of carriers Gilles Horowitz

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Multiple trapping & thermal release  Gate Voltage (charge carrier density) dependence –Upon aplied Vg a potential Vs develops at insulator-semiconductor interface –shift of E F towards E C –trapped carrier release becomes easier

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Multiple trapping & thermal release  Gate Voltage (charge carrier density) dependence

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Multiple trapping & thermal release  Alternative approach –effective mobility vs. effective charge density –Hall-effect measurements

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Multiple trapping & thermal release  Hall-effect results on rubrene single crystal Menard et al Podzorov, Menard, Rogers, Gershenson

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Summary  Drude  Bässler  Vissenberg Matters  MTR

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Device fabrication and measurement setups Part II:

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs OTFT, Fabrication and measurements

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Cryostat

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Parameter extraction and first results Part III:

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs OFET  some differences to conventional OFETs –can potentially operate in electron and hole accumulation mode

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs OFET  basic OFET operation –related to a capacitor

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs OFET output curve, logarithmicoutput curve, linear

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs green: Vd = 10V cyan: Vd = 45V Symobols: different devices 300 K 150 K

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs Thank You for Your Attention!

University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, Andrej Golubkov Charge transport in organic semiconductors and oTFTs transition between transport modes Trap dominatedIntrinsic