Ravi Sharma

1. Electrical Spin Injection into p-type Silicon using SiO2- Cobalt Tunnel Devices: The Role of Schottky Barrier Ravi Sharma Promoter Dr. SarojP. Dash Co- supervisor Andre Dankert Examiner Dr. ThiloBauch Co-Promoter Dr. Michel Houssa

2. Outline • Introduction & Motivation • Device Fabrication • Electrical measurements • Spin transport measurements • Summary

3. Spintronics Quantum property of electrons Spin +1/2 (clock wise) -1/2 (anti clockwise) Two possible spin states represent the "0" and "1" states in logical operations Advantages • * Low power consumption • - Energy scale for the charge interaction ~ eV, • - spin interaction ~100 meV. • Non-volatile memory • Integration between the logic and storage devices.

4. Spin polarization in ferromagnet E Minority Spin Majority Spin

5. Giant Magnetoresistance (GMR) P. Grünberg A. Fert Baibichet al. PRL 61, 2472(1988) Binaschet al.PRB 39, 4828 (1989) 2007 Nobel prize for Physics

6. Tunnel Magnetoresistance (TMR) Anti-parallel Co MgO CoFe Parallel 5K Mooderaet al. PRL 74, 3273 (1995) Parkin et al. Nature Mat. 3, 868 (2004) 300 K > 500 GB Data storage MRAM

7. Combining the best of both worlds Opportunities for new technology Silicon MOSFET - scaling for smaller and faster transistor 2008 2010 2012 2020 ? 45 nm 32 nm 22 nm Spin-Electronics Semiconductor chip Magnetic hard disc Process information Storage information

8. Spin transistor Ferromagnet Ferromagnet Gate Silicon Major challenges Advantage of Si Spintronics • Spin Injection • Transport • Detection • Manipulation Available technology Longer spin life time in Si • Low spin –orbit coupling • Low hyperfine interaction • Room Temperature • n- and p- type Si

9. Creation of Spin polarization in Si Electrical Injection Optical detection All electrical method at Room Temperature All optical method Dash, Nature 462, 491 (2009) Lampel, Phys. Rev. Lett. 20, 491 (1968) Jonker, Nature Phys. 3, 542 (2007)

10. My Thesis + h  Ferro magnet W V I ϕB Cobalt SiO2 • Ozone oxidized SiO2 • p-type Silicon (Boron Doping Dependence) • To study the effect of Schottky barrier width on spin injection and extraction • Fabrication of devices • Electrical characterization • Spin-transport measurement p- Silicon p-type Silicon SiO2

11. Outline • Introduction & Motivation • Device Fabrication • Electrical measurements • Spin transport measurements • Summary

12. Fabrication Cr/Au Cr/Au Cobalt SiO2 p-type Silicon

13. Fabrication BHF TB Silicon UV lamp 300 nm SiO2 O3 Silicon Au/Co Evaporation Au/Cr Au Au Au Au Co Co Co Co Au/Cr cont. by lift off patterning by ion-beam etching Silicon Silicon Silicon

14. Microscope images of device Contact holes Au/Co definition Cr/Au contact pads Cr/Au Cr/Au Au/Co/SiO2/p-Si

15. Microscope images of device Hall Bar

16. Outline • Introduction & Motivation • Device Fabrication • Electrical measurements • Resistivity and Hall measurement • Schottky barrier height and width • Spin transport measurements • Spin injection and detection in p-Si • Doping dependence studies • Summary

17. Electrical measurements Resistivity measurement d= distance between two contacts over which voltage is measured, W = channel width and t = thickness of the channel

18. Electrical measurements Hall measurement Hall voltage, Lorentz force,

19. Electrical measurements Silicon parameters

20. Schottky barrier

21. Schottky barrier I V V I Ferromagnet Cr/Au Cr/Au Tunnel barrier p- Silicon Au/Co/SiO2/p-Si

22. + h  Ferro magnet Schottky barrier W ϕB p-type Silicon SiO2

23. Schottky barrier eV Schottky barrier height is 0.23 eV

24. Schottky barrier

25. Outline • Introduction & Motivation • Device Fabrication • Electrical measurements • Resistivity and Hall measurement • Schottky barrier height and width • Spin transport measurements • Spin injection and detection in p++Si • Doping dependence studies • Summary

26. I-V measurement Co/SiO2 /p++ Si B doped 5 mOhm.cm Hole Extraction Hole Injection J-V curve Resistance at -200 mV = 1.3 KΩ

27. Spin Injection E ∆μ V I Ferromagnet Tunnel barrier Silicon

28. Spin detection by Hanle effect E ∆μ ∆μ Larmor frequency E ∆μ ̴ 0 • Spin-signal has a Lorentzian line-shape • The half width is inversely proportional to the spin-lifetime B

29. Spin Detection by Hanle effect P++ type Si/SiO2/Co 300 K

30. Spin life time and Polarization in p++ Si ∆V=929 uV Spin Lifetime τ = 49 ps Diffusion Length, LD > 63 nm ∆V=929 uV Δµ = 2.ΔV/TSP = 5.3 mV TSP = 0.35 300 K Spin polarization P=10.38 %

31. Spin Extraction P++ type Si/SiO2/Co B doped 5 mOhm.cm 300 K 800 mV

32. Bias dependence

33. Bias dependence TSP2= ) is the TSP for the detection is the TSP for the injection/extraction is spin lifetime is the spin-flip resistance in Si bulk channel. Assuming, TSP2 =()

34. Temperature dependence - 200 mV Weak temperature dependence indicates - true spin accumulation in silicon over the full temperature range

35. Outline • Introduction & Motivation • Device Fabrication • Electrical measurements • Resistivity and Hall measurement • Schottky barrier height and width • Spin transport measurements • Spin injection and detection in p++Si • Doping dependence studies • Summary

36. Doping Dependence 300 K W + h Ferro magnet ϕB p-type Silicon SiO2

37. Doping Dependence of Spin signal Spin injection Spin-signal increases with reducing Schottky barrier width

38. Bias dependence P++ type Si Direct tunneling Dominating As expected

39. Bias dependence P+ type Si

40. Bias dependence P+ type Si

41. Bias dependence P type Si

42. Bias dependence of Spin signal

43. Spin injection model • Direct tunneling (when RSC is small) • Two step tunneling (When RSC is large) Tran et al., PRL 102, 036601, 2009 Rtun RSC

44. Direct tunneling Hole Spin Injection Hole Spin Extraction Direct tunneling Dominating As expected

45. Spin reversal during extraction Localized state  Paramagnetic in nature

46. Spin reversal during injection

47. Summary • Large spin accumulation in p-type Si using SiO2 tunnel barrier ( ~ 10%) • Lower limit for Spin life time ( ~ 50 ps), Spin diffusion length > 60 nm • Higher doping in Si  higher spin accumulation, due to reduction in Schottky barrier width • Spin reversal phenomena observed when Schottky barrier width is higher • Schottky barrier width determines the spin transport behavior (sequential and/or direct tunneling)

48. Acknowledgement Michel Houssa Guido Groeseneken Saroj P. Dash Andre Dankert Goran Johansson ThiloBauch QDP members MC2 Staffs All my friends in Chalmers

49. Thank You!!!