Ravi Sharma Co-Promoter Dr. Michel Houssa Electrical Spin Injection into p-type Silicon using SiO 2 - Cobalt Tunnel Devices: The Role of Schottky Barrier Promoter Dr. Saroj P. Dash Co- supervisor Andre Dankert Examiner Dr. Thilo Bauch 1

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

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 * Low power consumption - Energy scale for the charge interaction ~ eV, - spin interaction ~100 meV. Non-volatile memory Integration between the logic and storage devices. Advantages 3

Spin polarization in ferromagnet E Majority Spin Minority Spin 4

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

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

Opportunities for new technology Silicon MOSFET - scaling for smaller and faster transistor 22 nm 32 nm45 nm Spin-Electronics Process information Semiconductor chip Combining the best of both worlds Storage information Magnetic hard disc 7

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

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

My Thesis p- Silicon SiO 2 Cobalt IV Ferro magnet  h + SiO 2 p-type Silicon W ϕBϕB  Fabrication of devices  Electrical characterization  Spin-transport measurement  Fabrication of devices  Electrical characterization  Spin-transport measurement  Ozone oxidized SiO 2  p-type Silicon (Boron Doping Dependence)  To study the effect of Schottky barrier width on spin injection and extraction 10

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

Fabrication p-type Silicon SiO 2 Cobalt Cr/Au 12

Fabrication 300 nm SiO 2 Silicon BHF TB Silicon UV lamp O3O3 Au Co Silicon Au/Cr Au/Cr cont. by lift off Au/Cr cont. by lift off Au Co Silicon Au/Co Evaporation patterning by ion-beam etching patterning by ion-beam etching 13

Microscope images of device Contact holes Au/Co definition Cr/Au contact pads Cr/Au Au/Co/SiO 2 /p-Si 14

Microscope images of device Hall Bar 15

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 16

Electrical measurements Resistivity measurement d = distance between two contacts over which voltage is measured, W = channel width and t = thickness of the channel Silicon p-10x10 -2 p11x10 -5 p+7.2x10 -5 p++5x

Electrical measurements Hall measurement 18

Silicon Doping concentration cm -3 Carrier mobility cm 2 V -1 s -1 Diffusion coefficients cm 2 s -1 p-1.34x x p5.4x x p+1.5x x p++2.1x x Electrical measurements Silicon parameters 19

Schottky barrier 20

Schottky barrier I V Cr/Au Au/Co/SiO 2 /p-Si p- Silicon Tunnel barrier Ferromagnet IV 21

Schottky barrier Ferro magnet  h + SiO 2 p-type Silicon W ϕBϕB 22

eV Schottky barrier Schottky barrier height is 0.23 eV 23

Siliconp-pp+p++ Schottky barrier width (nm) Schottky barrier 24

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 25

Hole Injection Hole Extraction J-V curve I-V measurement Resistance at -200 mV = 1.3 KΩ Co/SiO 2 /p++ Si B doped 5 mOhm.cm B doped 5 mOhm.cm 26

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

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

Spin Detection by Hanle effect P++ type Si/SiO 2 /Co 300 K 29

Spin life time and Polarization in p ++ Si ∆V=929 uV Spin Lifetime τ = 49 ps Spin polarization P=10.38 % 300 K ∆V=929 uV Δµ = 2.ΔV/TSP = 5.3 mV TSP =

Spin Extraction P++ type Si/SiO 2 /Co 300 K 800 mV 300 K 800 mV B doped 5 mOhm.cm B doped 5 mOhm.cm 31

Bias dependence 32

Bias dependence 33

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

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 35

Ferro magnet h + SiO 2 p-type Silicon 300 K Doping Dependence W ϕBϕB 36

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

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

Bias dependence P+ type Si 39

Bias dependence P+ type Si 40

Bias dependence P type Si 41

Bias dependence of Spin signal 42

Spin injection model Doping Total Junction RA (KΩ.μm 2 ) -200mV SiO2 barrier RA (KΩ.μm 2 ) p338 x x10 4 p+16 x x10 4 p++2.6 x x10 4 Direct tunneling (when R SC is small) Two step tunneling (When R SC is large) Tran et al., PRL 102, , 2009 R tun R SC 43

Direct tunneling Dominating As expected Hole Spin Injection Hole Spin Extraction Doping Junction RA (KΩ.μm 2 V Si -V FM Junction RA (KΩ.μm 2 V Si -V FM p++2.6 x x

Spin reversal during extraction Doping Junction RA (KΩ.μm 2 V V Si -V FM Junction RA (KΩ.μm 2 V Si -V FM p27.62 x x10 4 Localized state  Paramagnetic in nature 45

Spin reversal during injection Doping Junction RA (KΩ.μm 2 V Si -V FM Junction RA (KΩ.μm 2 V Si -V FM p338x x10 4 p x x

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) 47

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

Thank You!!! 49