1. Charge transport in organic semiconductors and organic field effect transistors Andrej Golubkov IF – Seminar, Graz, 5.11.2007

2. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 2 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Co-Workers  Egbert Zojer  Peter Pacher  Harald Etschmaier

3. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 3 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at 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

4. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 4 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Charge carrier transport models. Part I: overview based on reviews from Gilles Horowitz

5. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 5 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Comparison (Molecular) Crystal Covalent Metallic Gilles Horowitz

6. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 6 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Conjugated organic materials  sp2 hybridization of carbon  3 σ bonds from (2s, 2p x, 2p y )‏  1 π bond from 2p z

7. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 7 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Simple band transport: Drude model  free moving carriers, acceleration by external field  scattering at phonons, impurieties

8. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 8 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at  Temperature dependence of v th  Temperature dependence of scattering process: mean free path between phonons, charged impurities Simple band transport: Drude model W. Warta

9. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 9 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Polaron transport  Polarization by one single charge  dressed (by π- electros) charge residence time el. polarization time bandwidth bandgap Gilles Horowitz

10. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 10 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Polaron transport Gilles Horowitz Silinish E.A, Capek V.

11. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 11 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Polaron transport Silinish E.A, Capek V. Eg Charge modulated spectroscopy Peter J. Brown

12. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 12 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at 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

13. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 13 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at 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

14. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 14 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Hopping (polaron) Transport Pentacene 300 K180 K117 K A. R. Brown

15. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 15 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Multiple trapping & thermal release  Assumptions –carriers arriving at trap -> capture –release is thermaly activated –2 sorts of carriers Gilles Horowitz

16. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 16 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at 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

17. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 17 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Multiple trapping & thermal release  Gate Voltage (charge carrier density) dependence

18. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 18 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Multiple trapping & thermal release  Alternative approach –effective mobility vs. effective charge density –Hall-effect measurements

19. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 19 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Multiple trapping & thermal release  Hall-effect results on rubrene single crystal Menard et al Podzorov, Menard, Rogers, Gershenson

20. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 20 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Summary  Drude  Bässler  Vissenberg Matters  MTR

21. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 21 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Device fabrication and measurement setups Part II:

22. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 22 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at OTFT, Fabrication and measurements

23. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 23 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

24. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 24 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

25. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 25 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

26. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 26 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

27. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 27 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

28. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 28 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

29. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 29 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Cryostat

30. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 30 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at

31. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 31 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Parameter extraction and first results Part III:

32. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 32 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at OFET  some differences to conventional OFETs –can potentially operate in electron and hole accumulation mode

33. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 33 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at OFET  basic OFET operation –related to a capacitor

34. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 34 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at OFET output curve, logarithmicoutput curve, linear

35. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 35 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at green: Vd = 10V cyan: Vd = 45V Symobols: different devices 300 K 150 K

36. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 36 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at Thank You for Your Attention!

37. University of Technology Graz - Institute of Solid State Physics Professor Horst Cerjak, 19.12.2005 37 Andrej Golubkov Charge transport in organic semiconductors and oTFTs golubkov@sboxgolubkov@sbox.tugraz.at transition between transport modes Trap dominatedIntrinsic