1

Ravi Sharma

Co-PromoterDr. Michel Houssa

Electrical Spin Injection into p-type Silicon using SiO2- Cobalt Tunnel Devices:

The Role of Schottky Barrier

Promoter Dr. Saroj P. DashCo- supervisor Andre Dankert

ExaminerDr. Thilo Bauch

Outline

• Introduction & Motivation • Device Fabrication

• Electrical measurements

• Spin transport measurements

• Summary

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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

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Spin polarization in ferromagnet

E

MajoritySpin

MinoritySpin

4

Giant Magnetoresistance (GMR)

Baibich et al. PRL 61, 2472(1988)Binasch et al. PRB 39, 4828 (1989)

2007Nobel prize for Physics

P. Grünberg A. Fert

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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)

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Opportunities for new technology

Silicon MOSFET - scaling for smaller and faster transistor

?22 nm32 nm45 nm

201220102008 2020

Spin-Electronics

Process information

Semiconductor chip

Combining the

best of both worlds

Storage information

Magnetic hard disc

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Spin transistor

Major challenges

Spin Injection Transport Detection Manipulation

Room Temperature n- and p- type Si

FerromagnetGate

Silicon

Ferromagnet

• Low spin –orbit coupling • Low hyperfine interaction

Longer spin life time in Si

Available technology

Advantage of Si Spintronics

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Creation of Spin polarization in Si

All optical method Electrical InjectionOptical detection

All electrical methodat Room Temperature

Lampel, Phys. Rev. Lett. 20, 491 (1968)

Jonker, Nature Phys. 3, 542 (2007)

Dash, Nature 462, 491 (2009)

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My Thesis

p- Silicon

SiO2

Cobalt

I V

Ferromagnet

h+

SiO2

p-type Silicon

W

ϕB

Fabrication of devices

Electrical characterization

Spin-transport measurement

Ozone oxidized SiO2

p-type Silicon (Boron Doping Dependence)

To study the effect of Schottky barrier width on spin injection and extraction

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Outline

• Introduction & Motivation • Device Fabrication

• Electrical measurements

• Spin transport measurements

• Summary

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Fabrication

p-type Silicon

SiO2

Cobalt

Cr/AuCr/Au

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Fabrication

300 nm SiO2

Silicon

Silicon

BHF

TB

Silicon

UV lamp

O3

AuAuCo Co

Silicon

Au/Cr

Au/Cr cont. bylift off

AuAuCo Co

Silicon

Au/Co Evaporation

patterning by ion-beam etching

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Microscope images of device

Contact holes

Au/Co definition

Cr/Au contact pads

Cr/A

u

Cr/A

u

Au/Co/SiO2/p-Si 14

Microscope images of device

Hall Bar

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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

• Summary16

Electrical measurements

Resistivity measurement

𝑹𝒆𝒔𝒊𝒔𝒕𝒊𝒗𝒊𝒕𝒚 ,𝝆=𝑹𝑾𝒕𝒅

𝜴𝒎

d = distance between two contacts over which voltage is measured, W = channel width and t = thickness of the channel

Silicon Resistivity

p- 10x10-2

p 11x10-5

p+ 7.2x10-5

p++ 5x10-5 17

Electrical measurements

Hall measurement

Lorentz force, Hall voltage,

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Silicon Doping concentration

cm-3

Resistivity Carrier mobilitycm2V-1s-1

Diffusion coefficients

cm2s-1

p- 1.34x1015 10x10-2 466 11.65

p 5.4x1018 11x10-5 109 2.72

p+ 1.5x1019 7.2x10-5 57 1.42

p++ 2.1x1019 5x10-5 44 0.8

Electrical measurements

Silicon parameters

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Schottky barrier

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Schottky barrier

IV

Cr/Au

Cr/AuAu/Co/SiO2/p-Si

p- Silicon

Tunnel barrier

Ferromagnet

I V

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Schottky barrier

Ferromagnet

h+

SiO2

p-type Silicon

W

ϕB

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1exp

TnK

qVII

B

asat

TKTAAI

B

Bnsat

exp*. 2

TKTAA

I

B

Bnsat 1

*.log

2

)5617.8*( eslopeB eV

Schottky barrier

Schottky barrier height is 0.23 eV

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Silicon p- p p+ p++

Schottky barrier

width (nm)

736

13.52

8.26

7.02

𝑾 =√ 𝟐𝝐𝒔(𝝋𝑩+

𝒌𝑻 . 𝒍𝒏(𝒏𝒑

𝒏𝒊)

𝒒−𝑽 𝒂)

𝒒 .𝒏𝒑

Schottky barrier

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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

• Summary25

Hole Injection Hole Extraction

J-V curve

I-V measurement

Resistance at -200 mV = 1.3 KΩ

Co/SiO2 /p++ Si

B doped5 mOhm.cm

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Spin Injection

∆μ

E

Silicon

Tunnel barrier

Ferromagnet

I V

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2).(1

)0()(

sL

B

Spin-signal has a Lorentzian line-shape

The half width is inversely proportional to the spin-lifetime

Spin detection by Hanle effect

∆μ

E

E

∆μ = 0

∆μ

B

Bg B

L

Larmor frequency

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Spin Detection by Hanle effect

P++ type Si/SiO2/Co

300 K

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Spin life time and Polarization in p++ Si

∆V=929 uVSpin Lifetime τ = 49 ps

Spin polarization P=10.38 %

Diffusion Length,

LD > 63 nm

300 K ∆V=929 uVΔµ = 2.ΔV/TSP = 5.3 mV

TSP = 0.35

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Spin Extraction

P++ type Si/SiO2/Co

300 K800 mV

B doped5 mOhm.cm 31

Bias dependence

𝑺𝒑𝒊𝒏𝑹𝑨=∆𝑽 / 𝑱

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Bias dependence

𝑺𝒑𝒊𝒏𝑹𝑨=∆𝑽 / 𝑱=𝜸𝒅 𝜸 𝒊/𝒆𝒓𝒄𝒉=𝜸𝒅 𝜸 𝒊 /𝒆 𝝆 √𝑫𝝉 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.

TSP2= )

Assuming, TSP2 =()

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Temperature dependence

- 200 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

• Summary35

Ferromagnet

h+

SiO2

p-type Silicon

300 K

Doping Dependence

W

ϕB

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Spin-signal increases with reducing Schottky barrier width

Doping Dependence of Spin signal

Spin injection

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Bias dependence

Direct tunnelingDominating

As expected

P++ type Si

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Bias dependence

P+ type Si

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Bias dependence

P+ type Si

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Bias dependence

P type Si

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Bias dependence of Spin signal

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Spin injection model

Doping Total Junction

RA

(KΩ.μm2)

-200mV

SiO2 barrier

RA

(KΩ.μm2)

 

p 338 x104 1 x104

p+ 16 x104 1 x104

p++ 2.6 x104 1 x104

• Direct tunneling (when RSC is small)

• Two step tunneling (When RSC is large)

Tran et al., PRL 102, 036601, 2009

Rtun RSC

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Direct tunneling

Direct tunnelingDominating

As expected

Hole Spin Injection

Hole Spin Extraction

Doping Junction

RA

(KΩ.μm2)

@-200mV

VSi-VFM

Junction

RA

(KΩ.μm2)

@+200mV

VSi-VFM

p++ 2.6 x104 1.068 x104

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Spin reversal during extraction

Doping Junction

RA

(KΩ.μm2)

@+200m

V

VSi-VFM

Junction

RA

(KΩ.μm2)

@+800mV

VSi-VFM

p 27.62 x104 0.678 x104

Localized state Paramagnetic in nature45

Spin reversal during injection

Doping Junction

RA

(KΩ.μm2)

@-200mV

VSi-VFM

Junction

RA

(KΩ.μm2)

@-800mV

VSi-VFM

p 338x104 151.9 x104

p+ 16.68 x104 14.23 x104

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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)

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Saroj P. Dash

Andre Dankert

Michel Houssa

Guido Groeseneken

Acknowledgement

Thilo Bauch

QDP members

MC2 Staffs

Goran Johansson

All my friends in Chalmers

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Thank You!!!

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