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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
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
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
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 nm32 nm45 nm
201220102008 2020
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
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
8
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)
9
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
10
Outline
• Introduction & Motivation • Device Fabrication
• Electrical measurements
• Spin transport measurements
• Summary
11
Fabrication
p-type Silicon
SiO2
Cobalt
Cr/AuCr/Au
12
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
13
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
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
• 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,
18
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
19
Schottky barrier
20
Schottky barrier
IV
Cr/Au
Cr/AuAu/Co/SiO2/p-Si
p- Silicon
Tunnel barrier
Ferromagnet
I V
21
Schottky barrier
Ferromagnet
h+
SiO2
p-type Silicon
W
ϕB
22
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
23
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
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
• 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
26
Spin Injection
∆μ
E
Silicon
Tunnel barrier
Ferromagnet
I V
27
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
28
Spin Detection by Hanle effect
P++ type Si/SiO2/Co
300 K
29
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
30
Spin Extraction
P++ type Si/SiO2/Co
300 K800 mV
B doped5 mOhm.cm 31
Bias dependence
𝑺𝒑𝒊𝒏𝑹𝑨=∆𝑽 / 𝑱
32
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 =()
33
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
36
Spin-signal increases with reducing Schottky barrier width
Doping Dependence of Spin signal
Spin injection
37
Bias dependence
Direct tunnelingDominating
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.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
43
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
44
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
46
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