CMD WS Osaka, 15 September, 2017

Semiconductor spintronics with high-quality
ferromagnet/Ge interface: Expectation for computational science

Contents
1. Expectation for Ge spintronics
2. Crystal growth of Heusler alloys on Ge

WL$>'_©¤¢¥;V: £«¡ª¢ =B
IC@,%3. Spin injection into n-Ge and p-Ge

Osaka University
Kohei Hamaya

4. For an enhancement in MR ratio

RXS?!=B@
浜屋 宏平

Developments of semiconductor technologies
http://www.intel.com/

Why Ge ?
Mobility

Si

Ge

GaAs

InAs

Electron2(cm /Vs)

1450

3900

8000

33000

Hole
(cm2/Vs)

500

1900

400

460

Si-LSI performance

Metal
http://www.intel.com/

High-k
SiGe
SiGe
Si

SiO2
(1.2 nm)
SiGe

s-Si

Novel technologies !!

High-k/metal gateSiGen-Ge(111) > n-Ge(100)Strained Si
Tri-gate

aw
sl
re'
o
ソース
Mo

gy
nolo
Tech
ゲート

ter
boos

ドレイン

ゲート

ソース

ドレイン

絶縁膜

Si-MOSFET

90 nm

酸化膜

Si

45 nm

Si基板

・・・14 ~ 10 nm

http://www.intel.com/

Gate length

C. H. Lee et al., IEEE Trans. Elec. Dev. (2011).

n-Ge

Why Ge ?

Why Ge ?

Mobility

Si

Ge

GaAs

InAs

Electron2(cm /Vs)

1450

3900

8000

33000

Hole
(cm2/Vs)

500

1900

400

460

High affinity
for photonics
0.66 eV

Optical communication
wavelength

on Si
J. R. Chelikowsky and M. L. Cohen, PRB 14, 556 (1976).

Ge CMOS in 2014
H. Wu et al., 2014 International Electron Device Meeting (IEDM).

D. Wang et al., TSF 602, 43 (2016).

What is Spintronics ?

Why Ge ?
Mobility

Si

Ge

GaAs

InAs

Electron(cm2 /Vs)

1450

3900

8000

33000

Hole
(cm2 /Vs)

500

1900

400

460

Ge CMOSGe Photonics

sGe

sGe

r|Xxxv|v XXXX
Spintronics is an emerging technology exploiting both the intrinsic
spin of the electron and its associated magnetic moment, in
addition to its fundamental electric charge, in solid-state devices.

hxv|vXv{uzx

BOX
Si

rx|vwvX
xxv|vrby Prof. K. Sawano+ Spintronics

XXXXXXXr|X
XZXXXXXXXXXXX[r||vn

Spin-dependent transport (MR)Spintronics for memory technologies
183713-2

Integration of spin dependent transport

Ferromagnet / Nonmagnet / Ferromagnet( eg., Fe / Cu / Fe )
r

r

lX
x | uvxX

puuxXvy|zu|
n

n

r

n

`
Nonvolatilememoryk|z{Xx | uvxg|]uuxvy|zu|
n

a

r

Spin MOSFET by S. Sugahara and M. Tanaka, APL (2004).
Low power consumption + Nonvolatile memory

Gate

Ge
Si
Ge channel for high performance

J. Appl. Phys. 113, 183713 (2013)

molecular beam epitaxy (MBE) at 130 & C, where we cothat the temperature dependence of the spin signals in ourElectronevaporated
Charge+ Knudsen
Spincells.46,47 We observed aFe3Si/nþ-Ge/n-Ge devices is dominated by the temperature
Fe and Si using
dependence of the creation of spin accumulation in n-Ge
high-resolution cross-sectional transmission electron microAs a result, the Fe3Si/nþ-Ge
using the Fe3Si/nþ-Ge Schottky-tunnel contacts. We willgraph (TEM)onof Fe
Si
platform
3Si/Ge(111).
simply comment on the attention to the development ofheterointerface was atomically flat, leading to the reduction insemiconductor spintronic devices.
the presence of interface states.16,37–39 We also observed nanobeam electron diffraction patterns in the Fe3Si layer and in nþGe near the interface. It should be noted, in the Fe3Si layer, that
II. DEVICES WITH SCHOTTKY TUNNEL CONTACTS
there are h111i and h113i superlattice reflections resulting
from the presence of D03-ordered structures. Thus, theOur lateral devices with n-Ge channels have SchottkyHeusler-compound electrodes were very high quality.46,47
tunnel contacts. Figures 1(a) and 1(b) show schematic diaAlso, the quality of nþ-Ge layer was almost equal to that ofgrams of the fabricated devices with Fe3Si/ nþ-Ge contacts forconventional Ge substrates.
three-terminal Hanle-effect measurements and nonlocal spinIn order to align the magnetic moments in the in-planevalve measurements, respectively. The followings are fabricadirection for the three-terminal Hanle-effect measurements,6tion processes of these devices. First, we formed a phosphorousa polycrystalline Co layer with a thickness of "25 nm was(P)-doped n-Ge(111) channel (n " 5 # 1017 cm$3) with a thickdeposited on the Fe3Si layer by using electron beam evaporaness of "100 nm on non-doped Ge(111) substrates (q ¼ "40 X
tion. Conventional processes with photolithography, Arþ ioncm) by using an ion implantation technique. After the fabricaSpin-RAM
milling, and reactive ion etching were used to fabricate ation of the n-Ge(111) channel, the nþ-Ge(111) layer consistingNonvolatile+ HighNonvolatile
three-terminal lateraldevice. Eachcontactspeed
denoted by 1, 2,
of Sb d-doped layer and a 5-nm-thick Ge epitaxial
layer were
, 40 #(2004).
200 lm2,
3 has a lateralS.
dimension
ofand
100M.
# Tanaka,
200 lm2APL
theChappert
doping densityof Sb Mat.or (2007).
grown by MBE at 400 & C,39 where C.
Sugaharaetal.,Natureor 100 # 200 lm2, respectively. The edge-edge distancewas 2 # 1014 cm$2. Then, a 10-nm-thick Fe3Si epitaxial filmby powerOFF!!
betweencontacts =>1 and
2 or contacts
2 and 3 was 40 lm, andwas grown on the nþ-Ge(111) layer by low-temperatureStandþ-Ge(111) andlayer wasremoveddevices
by Arþ ion milling.
Ultra low power consumptiontheinn Si-LSI
relatedUsing the three-terminal geometry shown in Fig. 1(a), we
measured current-voltage (I21-V23) characteristics at theinterface in Fig. 1(c). The I21-V23 curves show almost no rectifying behavior for all the temperatures. This means thattunneling conduction of electrons through the Fe3Si/nþ-Geinterface is dominant although the tunneling current canchange with temperature variations, giving rise to thedecrease in the interface resistance below 200 K. Similar
temperature dependence has already been observed in a previous study of Co/insulator/nþ-Ge junctions.15,42
To observe lateral spin transport in n-Ge(111), we alsofabricated four-terminal lateral spin valves as shown in Fig.
・Ni/n-Ge/n-AlGaAs
1(b). Although the used Fe3Si/nþ-Ge/n-Ge structure is fabriC. Shen et al., Appl. Phys. Lett. 97, 162104 (2010).
cated in the same sample grown, the contact sizes for the
spin injector and spin detector are markedly small compared・CoFe/MgO/n-Ge
to the three-terminal device. The lateral dimensions of the
0.5 # 2.0 lm2,
5 areLett.
0.3 99,# 2.0
lm2 and
K. contact
R. Jeon 4etandal., contact
Appl. Phys.
162106(2011).
respectively. The edge-edge distance between contacts 4 and・Fe/MgO/p-Ge
5 was less than 0.4 lm [Fig. 1(d)]. For four-terminal lateral
weCommun.
did not 151,
depositpolycrystalline
Fe3Si/n-Ge
H. spin-valve
Saito et al., devices,
Solid State
1159a(2011).
Co layer on the Fe3Si layer to avoid the influence of the animagnetoresistance on the spin transport measure・Fesotropic
3Si/n-Ge
ments.48 In the three- and four-terminal measurements,
K. Kasahara et al., J. Appl. Phys. 111, 07C503 (2012).
external magnetic fields perpendicular to the film plane (Bz)and parallel to the film plane (Bx) were applied, respectively.
・Fe/MgO/p-Ge
It should be noted that we could not measure the HanleS. effectIba et curvesal., Appl.
Express 5, 053004(2012).
inPhys.
the four-terminal
geometry
because of theabsence of the Co layer.48 Namely, it was very difficult for・Py/p-Ge
our devices to obtain the Hanle-effect signals unfortunately.

Spin injection into Ge

Spin signal(mΩ)

Spin injection and detection for low power consumption

Hamaya et al.

M. Koike et al., Appl. Phys. Express 6, 023001 (2013).

150 K
Si substrate for low costIII. RESULTS AND DISCUSSION
・CoFeB/MgO/n-Ge

FIG. 1. Schematic diagrams of lateral (a) three-terminal and (b) fourterminal devices with high-quality Fe3Si/nþ-Ge contacts. (c) Temperaturedependent I21-V23 characteristics measured for the three-terminal device. (d)Enlarged scanning electron micrograph of the contacts for the four-terminal
device.

	
(Oe)
Field

A. Roias-Sanchez
Creation of spin
accumulation
J.-C.
et al.,
Phys. Rev. B 88, 064403 (2013).

・Py/n-Ge/Pd
three-terminal
device, as illustrated in Fig. 1(a). When the
We first focus on spin-accumulation signals for a lateral

S.Dushenko et al., Phys. Rev. Lett. 114, 196602 (2015).

[This article isK.
copyrighted
indicatedin thearticle.
Reuseof AIP
content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:
Hamaya as
et al.,
J. Appl.
Phys.
113,
183713(2013).
133.5.11.13 On: Sat, 07 Dec 2013 06:38:55

A = 1.5 µm , and L = 420 nm. The possible methods for
improving the spin injection efficiency include the optimization the MgO film thickness and the Ge surface passivation
technique.
Figure 2(b) shows the nonlocal spin valve signals measured
on device A at different temperatures. The signal is observable
up to 225 K. Figure 2(c) summarizes the #RNL as a functionof the temperature for device A. The #RNL is weakly
dependent on temperature at low temperature region, which
increases slightly from 0.83 $ at 1.5 K to 1.04 $ at 10 K,
and then decreases to 0.72 $ at 30 K. However, as thetemperature further increases, the #RNL drops abruptly and is
Fe/MgOn-Ge
LSVs dependence
not observable for
T > 225 K. -Similar
temperatureof #RNL is also observed in device B with a longer transportchannel [L = 1 µm, as shown in Fig. 2(d)].

Reliable spin transport in n -Ge (1016 cm-3)

Spin MOSFET by S. Sugahara and M. Tanaka, APL (2004).

Y. Zhou et al., Phys. Rev. B 85, 125323 (2011).

Spin injection and detection for low power consumption

C. Non-local Hanle measurement

To further explore the spin transport properties in Ge, we
perform the nonlocal Hanle measurement. In this measurementa small transverse [in z direction, as shown in Fig. 1(b)]magnetic field (Bz ) is PHYSICAL
applied toREVIEW
induceB theprecession
84, 125323(2011) of
the injected spin by the Hanle effect.21,30 The precession
and dephasing of the spins during their transport in Ge is017 cm−3 , 1 × 1018 cm−3 , anderefore the spin detection at
manifested as the magnetic field (Bz ) dependence of thein accumulation in the graded
VNL (or RNL , equivalently). Figure 3(a) shows the Hanle
efficiency of the Fe/MgO/Ge
precession curves of device B at 4 K under a reverse bias
o be 0.23% using Eq. (1) inof −130 µA. The red and black symbols are for signals taken
ength λsf = 0.58 µm (calcuwhen the injector/detector magnetizations are in parallel andasurement), Ge conductivity
antiparallel configurations, respectively. A spin lifetime (τs )Ref. 29), cross-sectional area
m. The possible methods forof 1.08 ns is extracted by fitting the Hanle curves based on theficiency include the optimizaone-dimensional (1-D) spin drift diffusion model,18,19,22 undernd the Ge surface passivation
which
#
"
! ∞
al spin valve signals measured
1
L2
RNL ∝ ±
cos(ωL t)
exp −√tures. The signal is observable
4Dt
4π
Dt
0
arizes the #RNL as a function%$
e A. The #RNL is weakly
t
dt.
(1)
× exp −
w temperature region, whichτs
at 1.5 K to 1.04 $ at 10 K,$ at 30 K. However, as the In the previous equation, + (−) sign is for the parallelhe #RNL drops abruptly and (antiparallel)ismagnetization configuration, D is the diffusion
milar temperature dependence
constant, ωL = gµB Bz /h̄ is the Larmor frequency (where g =vice B with a longer transport
1.6 is the Landé g-factor for Ge,31 µB is the Bohr magneton,n Fig. 2(d)].

and h̄ is the reduced Planck constant). The temperaturedependent spin lifetimes for device A and device B (obtained
le measurement
under reverse biases) are shown in Fig. 3(b) in solid circles
ransport properties in Ge, we
and open squares, respectively. Similar to the temperaturesurement. In this measurement
dependence of #RNL , the dependence of the spin lifetime
ion, as shown in Fig. 1(b)]on temperature is rather weak at low temperatures, while it
to induce the precession of
becomes much stronger as the temperature increases. This cane effect.21,30 The precession
ring their transport in Ge be
is explained in the following. For Ge, which possesses thelattice-inversion symmetry, the spin relaxation is predicted toeld (Bz ) dependence of theGe
Si
FIG. 3. (Color online) (a) Nonlocal Hanle precession curves
measured on device B at 4 K with a DC injection current of −130 µA.
The red and black symbols are for signals measured when theinjector and detector are in parallel and antiparallel configurations,
respectively. The solid lines are fitting based on the 1-D spin-drift
diffusion model, from which the spin lifetime is extracted to be
1.08 ns. (b) Temperature-dependent spin lifetimes measured on device
A (solid circles) and B (open squares), respectively.

Detection temperature : < 100 K

Spin polarization (efficiency) ~ 0.4 %1. Highly efficient and reliable spin injection and detection
2. Understanding spin relaxation mechanism in Ge

Observation of MR・・・No

be dominated by the Elliot-Yafet mechanism,12,13 under which
the spin relaxation rate (1/τs ) is proportional to the momentum
relaxation rate. The two major sources of momentum
relaxation are the ionized impurity scattering and the phonon
scattering. And the temperature dependence of the ionized
impurity scattering rate is found to be much weaker than thatof the phonon scattering in n-type Ge.29 It is expected thatat low temperature region, ionized impurity is the dominantContents

igure 3(a) shows the Hanle
at 4 K under a reverse bias
symbols are for signals taken
netizations are in parallel andpectively. A spin lifetime (τs )the Hanle curves based on thet diffusion model,18,19,22 under#"L2cos(ωL t)
exp −
4Dt
%
dt.

Gate

Spin MOSFET application

Spin MOSFET by S. Sugahara and M. Tanaka, APL (2004).

125323-4

1. Expectation for Ge spintronics
Gate
FIG. 3. (Color online) (a) Nonlocal Hanle precession curves
measured on device B at 4 K with a DC injection current of −130 µA.
The red and black symbols are for signals measured when theinjector and detector are in parallel and antiparallel configurations,
respectively. The solid lines are fitting based on the 1-D spin-drift
diffusion model, from which the spin lifetime is extracted to be
1.08 ns. (b) Temperature-dependent spin lifetimes measured on device
A (solid circles) and B (open squares), respectively.

2. Crystal growth of Heusler alloys on Ge(1)(−) sign is for the parallel
nfiguration, D is the diffusion
Larmor frequency (where g =,31 µB is the Bohr magneton,
constant). The temperaturevice A and device B (obtainedn in Fig. 3(b) in solid circles. Similar to the temperatureendence of the spin lifetime
at low temperatures, while it
mperature increases. This can
For Ge, which possesses thespin relaxation is predicted to

3. Spin injection into n-Ge and p-Ge
be dominated by the Elliot-Yafet mechanism,12,13 under which
the spin relaxation rate (1/τs ) is proportional to the momentum
relaxation rate. The two major sources of momentum
relaxation are the ionized impurity scattering and the phonon
scattering. And the temperature dependence of the ionized
impurity scattering rate is found to be much weaker than thatof the phonon scattering in n-type Ge.29 It is expected thatat low temperature region, ionized impurity is the dominant

4. For an enhancement in MR ratio

125323-4

Ferromagnet
Spin injection

Ge
channelFerromagnet
Spin detection
Spin transport

Observation of spin dependent transport
in Ge is required !!
Source and drain structures are very important !!

Ferromagnetic metal on Ge

Ferromagnetic metal on Ge

Germanidation reaction !!

Germanidation reaction !!
r|X|}xv

r|X|}xv

Ferromagnetic metal
Germanides= Nonmagnets

Ferromagnetic metal

Insulator

rvux|zjx

GeSpin injection into GenX |XxyyxvXYY

Large parasitic resistance == low power consumption

Spin injection into Ge w/o using insulators

For improvement of spin injection/detection .....

(Pinj

jx

Ge

Pdet)1/2 〜 0.4 %ΔµGeConventional Ferromagnet

Ge

+

-Ge
n Si

Fe/MgO - n-Ge LSVs
Y. Zhou et al., Phys. Rev. B 85, 125323 (2011).

£«2
Δµ

n+Si
-Ge

High Spin injection/detection
efficiency is required !!

7®a.*H'XYY
Manygroups utilized this method.
Y. Zhou et al., Phys. Rev. B 85, 125323 (2011).

Highly efficient spin injection !!

K. R. Jeon et al., Appl. Phys. Lett. 99, 162106 (2011).

Highly spin-polarized
Ferromagnet

nxXwxxxXyX |X|}xv|X|Xjx

Ferromagnetic Heusler alloys on Ge(111)Ferromagnetic Heusler : Fe3Si ( Fe2FeSi )

X

Fe
Y
Z

0.563 nm~0.56 nmFe~0.56 nmSiGe

L21 - ordered X2YZ

Atomic arrangement matching !
NOT Half-Metallic

Fe × 2
X×2

Y×1

Fe × 1

Si × 1
Calculation ( Prof. H. Itoh )

Ge

Z×1

Fe3Si on Ge(100),(110),(111)

Epitaxial Growth of Fe3Si on Ge(111)
Low temperature MBE

Ge(100)Ge(110)Ge(111)

poly

poly

epi

Ultra high vacuum(〜10-8 Pa)
RHEED
EB gun 

substrate

RHEED
ScreenControl ofstoichiometry

Fe
Kc

ell

K. Hamaya et al., Phys. Rev. B 83, 144411 (2011).
S. Yamada, KH et al., Phys. Rev. B 84, 174406 (2012).

Si
ell

Kc

Fe3Si(100)

Ge(100)

Fe3Si(110)

Ge(110)

Fe3Si(111)

Ge(111)Fe3Si/Ge(111) interface

The degree of the crystal ordering of Fe3Si films
57Fe Mossbauer spectra@RT*

by Prof. Mibu
(Nagoya Institute of Technology)
Fe(I)
Fe(II)Fe3Si

Si

D03 - Fe3Si

Ge(111)

Ideal DO3-ordered structure, site 1: site 2 = 66.6 : 33.3
1 nm

Our samples, site 1: site 2 = 44.2 : 22.4

S. Yamada, KH et al., Phys. Rev. B 84, 174406 (2012)

K. Hamaya et al., Phys. Rev. B 83, 144411 (2011).

Co2FeAlxSi1-x on Ge(111)

Half metallic Co2FeAlxSi1-x

CoFe

Al or Si

L21- Co2FeAl1-xSix
Spin resolved DOS

L21- Co2FeAl1-xSix

Low temperature MBE
Ultra high vacuum(〜10-8 Pa)
RHEED
EB gunCo

Fe

Fe × 1Ge

Al or Si × 1 

substrateA

Co2FeSi0.5Al0.5 : Half metallic DOS
T. M. Nakatani et al. J. Appl. Phys. 102, 033916 (2007).

Co × 2

Fe × 1RHEED
ScreenAl or SiK

Co × 266 ~ 67 % ordered

Al or Si × 1

ce

ll

D
B
K cell

C

K

ce

ll

K cellNon-stoichiometric depositionGe

S. Yamada, KH et al., Appl. Phys. Lett. 105, 071601 (2014).
K. Tanikawa, KH et al., Thin Solid Films 557, 390 (2014).

Co2FeAlxSi1-x on Ge(111)

Co2FeAlxSi1-x on Ge(111)
L21- Co2FeAl1-xSix

Low temperature MBE
Ultra high vacuum(〜10-8 Pa)
RHEED
EB gun 

substrate

RHEED
ScreenHeusler surface

Co

A
K

ce

ll

D
B
K cellGe(111) surface

C

K

ce

Fe

Al or Si

Fe × 1

Al or Si × 1ll

K cellCo × 2

Non-stoichiometric deposition
S. Yamada, KH et al., Appl. Phys. Lett. 105, 071601 (2014).

Ge
Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).

K. Tanikawa, KH et al., Thin Solid Films 557, 390 (2014).

2

Co2FeAlxSi1-x on Ge(111)nmHigh-quality Heusler-alloy/Ge heterointerface

HAADF-STEM imager|X|}xv

B2

r|X|}xvX2YZ(Heusler alloy)

rvux|z

0.7 nm

0.7 nm

Ge

B2
+
Ge

Z. Nedelkoski, KH, V. Lazarov et al., Sci. Rep. 6, 37282 (2016).

2 nm

Ge(111)

Z. Nedelkoski, KH, V. Lazarov et al., Sci. Rep. 6, 37282 (2016).

jx
r|X
u|u|jxnX |X
u|u|XYY

Spin resistance mismatch between metal and SC

Contents

  1. Expectation for Ge spintronics

Ie




Spin absorption

2. Crystal growth of Heusler alloys on Ge

qx | ||

r|Xx | uvx

3. Spin injection into n-Ge and p-Ge

ρ×λ
Rs 
(1-P2) S

P = 1 (Half metal)

hyyxv|xXuxu

S. Takahashi and S. Maekawa, Phys. Rev. B 67, 052409 (2003).
T. Kimura et al., Phys. Rev. B 72, 014461 (2005).

r|Xu|u|

4. For an enhancement in MR ratior|Xw|yy |Xxz{

nonmagnetic SC

Ie

Tunnelbarrier

Suppression of spin absorption
Creation of spin polarization in SC

Schottky barriers in metal/n-Ge

Schottky barriers in metal/n-Ge

Fe3Si/n-Ge (~ 1015 cm-3)

Fe3Si/n-Ge (~ 1015 cm-3)

V (V)

IR
qφ
= SA** exp(− )T2kT1000/T [K-1]

K. Yamane, KH et al., Appl. Phys. Lett. 96, 162104 (2010).

330 K| J |/T2 (A/cm2K2)

270 K

Φ = ~ 0.45 eV| J | (A/cm2)| J | (A/cm2)| J |/T2 (A/cm2K2)

330 K

Φ = ~ 0.45 eV

Thermionic emission
270 K

V (V)

IR
qφ
= SA** exp(− )T2kT1000/T [K-1]

K. Yamane, KH et al., Appl. Phys. Lett. 96, 162104 (2010).

Spin injection efficiency is not so high ....

Schottky tunnel contacts with Sb delta-doping

Spin injection into Ge for spin-MOSFET

Tunneling

Ge

n+Si
-Ge

+

-Ge
n Si

Thermionic emission
Many groups utilized this method.
Y. Zhou et al., Phys. Rev. B 85, 125323 (2011).

Highly efficient spin injection !!

K. R. Jeon et al., Appl. Phys. Lett. 99, 162106 (2011).

Delta doping for Ge

Nonlocal voltage measurements

Delta doping of Sb
Efficient spin injection& Low RAK. Sawano, KH et al., Appl. Phys. Lett. 97, 162108 (2010).

Nonlocal voltage measurements

M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985).
F. J. Jedema et al., Nature (London) 416, 713 (2002).

M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985).
F. J. Jedema et al., Nature (London) 416, 713 (2002).

Spin precession (Larmor precession)

Nonlocal'Hanle'curve
Nonlocal'spin'signal

Fabrication processGe

Ge

LT-Ge layer (~

HT-Ge la30 nm, 3

Si(111) su
bstrate

50 ℃)

substrayer (~70

nm, 700℃)

0.5Si0.5(10 nm,Co2FeAl

Si

RT)

Si(111) su℃)

P δ doping + ultrathin Si layer

bstrateLateral spin device with n-Ge

FM spin injector/detector

FM spin injector/detector

M. Yamada et al.,APL 107, 132101 (2015).

d = 0.3 µm〜 1.9 µmd = 0.3 µm〜 1.9 µm

M. Yamada, KH et al., Mat. Sci. Semicon. Proc. 70, 83 (2017).

M. Yamada, KH et al., Mat. Sci. Semicon. Proc. 70, 83 (2017).

4.0
J (104 A/cm2)n+-Ge
δ-P + Sid

Ohmic contacts formation(EB lithography, EB evaporation)

FM contacts fabrication(EB lithography, Ar+ milling)

Lateral spin device with n-Ge

M. Yamada et al.,APL 107, 132101 (2015).

m

Si(111) su
bstrateSi(111) su

bstrateGrowth of n+-Ge layer

Au/Ti

P δ doped Ge withinsertion
ultrathinlayer (~1Si
0 nm, 35
0 ℃)

Si(111) su

teMesa fabrication(EB lithography, Ar+ milling)Appl. Phys. Lett. 105, 071601 (2014).

5µnm, 350

Growth of CFASSi

7µyer (~70

P

bstratemGe

Si(111) su

bstrateGrowth of HT-Ge layerδ-doping

n +-Ge laAlbstrate

P

Ge

Fe

Co

Si(111) su

Growth of LT-Ge layerSi(111)Fabrication process

0

-4.0
-0.2

8K
30 K
50 K

77 K
100 K
125 K

-0.1

0
Vint (V)0.1

0.2

Highly spin polarized Co2FeAlxSi1-x

Highly spin polarized Co2FeAlxSi1-x

77 K d = 0.4 µm I = -1.0 mA

50

CoFe(10nm)

CFAS(10nm)

0
-1.0

-60
-100

-20
-40

-2.0
-3.0
-100

|ΔRNL| (mΩ)ΔRNL (mΩ)

1.0
ΔRNL (mΩ)

-40

40

0

-20

0
By (mT)

100

-40

0
By (mT)

-1
-40

20

0
50

40

0

-2

RA ~ 280 Ωµm2

10

-60

RA ~ 560 Ωµm2

30

100

0
By (mT)

295 K

1

100

3

0
By (mT)

40

Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).

CFAS
CFAS
CFAS/CF

150

200

250

300

T (K)

Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).

Fujita, KH et al., Phys.3Rev. B 94, 245302 (2016).
± 0.01 µm. The observed weak temperature dependence[23]. As this study clearly indicatesY.that
there is almostof λGe and λGe = 0.52 ± 0.01 µm at 125 K are inconno contribution of τphon to τs in Fig. 3(b), we can under0.01theµm.expected
The observed
weak temperaturedependence[23]. τAswithin
this study
clearly
thereKisasalmost
sistent ±withtemperaturedependence
and
stand
a rangeofindicates
8 K ≤ Tthat≤ 125
a result
s
of
λ
and
λ
=
0.52
±
0.01
µm
at
125
K
are
inconnocontribution
of
τ
to
τ
in
Fig.
3(b),
can under- as
Ge
Ge
phon
s
λGe ∼ 1.3 µm at 130 K in Ref.[22]. From the λGe valueof only the donor-induced spin relaxationwemechanism,
sistent with the expected temperature dependence andstand τs within a range of 8 K ≤ T ≤ 125 K as a result
for each temperature,
we can also clarify τ s by using thetheoretically
predicted in Ref. [23]. Actually, the exper1-x the donor-induced
λGe ∼ 1.3√µm at 130 K in Ref.[22]. Fromthe λ2Ge value x of only
spin relaxation mechanism, as
relation,
λ
=
Dτ
,
where
D
is
the
diﬀusionconstant.
imentaldata
in Fig. 3(b)are[23].
approximatelyGesfor each temperature,
we can also clarify τ s by using thetheoretically predicted
in Ref.
Actually, theconsistentexper√
Becausethis work
degenerated
semiconductors,
we
with
the
theoreticallycalculatedτvalue consistentof ∼0.12 ns
imp
relation,
λGe used
= Dτ
,
where
D
is
the
diﬀusionconstant.
imental
data
in
Fig.
3(b)
are
approximatelys−3
P. Li et al., Phys. Rev. B 86, 085202 (2012).
100 Kthis200
K in
250whenK
shouldestimate
D workvaluesfromEq. (4)
Ref.[39].
Thewe
aB = calculated
6.45 nm [2],n value= 8.2 of× ∼0.121018 cm
Becauseuseddegenerated
semiconductors,
with wetheassume
theoretically
τimp
ns ,
10
10
20
n-Ge
Y. Song et al., Phys. Rev. Lett. 113, 167201 (2014).
18−3
estimated
D as
a functionof temperatureshown in∆sonm=[2],0.11aB , , meshouldestimate
D values
from Eq. (4) was
in Ref.[39].
The mwhen
we assumeaBand= 6.45n =meV,
8.2 ×where
10 cm
e = 0.16m
0 [40],
thethe D was
value
and
and
are 0theradius,the electron
estimated D Material[29].
as a functionofUsing
temperatureme ∆=so0.16m[40],electronand ∆soBohr= 0.11
meV, where
aB , me ef10 Supplemental
5
5 shown in
Impurity
Intravalley
Intervalley
the inset
Supplemental
Material[29].
Using the τDvalue
and fectiveand ∆masstheheavily
electron
Bohr Ge,
radius,µe , in theof Fig. 3(a),we can calculate
each
doped
andthetheelectronenergy efscale
so are inscatterings atscattering
scattering
µ
,
in
the
inset
of
Fig.
3(a),
we
can
calculateτateach
fectivemass
inheavily
doped
Ge,
and
the
energyscaletemperature,
as displayed
spin-orbit coupling induced splitting of the triply degene
11
1
10 in Fig. 3(b), where 0τss as a0
0.6
temperature,
as displayedin Fig.
3(b),whereτs as a erate
spin-orbit
inducedof thetriplyfunctionof temperaturein previous
works
is also
replot1s(T 2coupling) donor statein splittingGe, respectively.
In degenaddition,
+
+
=
τGe
τimp
τinterτintrafunctionAsof statedtemperaturein previous works is also replot1s(T 2 ) donor
in meV,Ge, respectively.
In addition,
ted [19–22].
innot
if erate
we assume∆so =state
0.062
we can estimateτimp of-5 introduction, the τs does
-5
-10
ted
[19–22].
As
statedinintroduction,
the
τ
does
not
if
we
assume
∆
=
0.062
meV,
we
can
estimate
τ
of
s
so
imp
depend on n yet. Note that the obtained τs values are∼0.47 ns. Note that the assumed ∆so values are close todepend on n yet. Note that the obtained τs values are∼0.47 ns. Note that the assumed ∆so values are close to
Theoretical curve
markedly smaller than thosein previous works -10[19–22].
∼0.03 meV for P doped Si and muchsmaller than the-10-20
markedlysmallerthan-40those in0 previous
works [19–22].
∼0.03
for P doped Si and much smaller than the
+
-40
40
0
40
-40
40 meV induced
00.4
We canalso
extract
the
τ
and
D
for
n
-Ge
by
fitvalley-orbit
singlet-triplet
splitting
in
P
doped
+
s
BWe
(mT)
Bz (mT)valley-orbit induced singlet-triplet splitting in P doped
can also extract the Bτzs (mT)and D for n -Ge by fitz
ting theting
Hanle-eﬀectcurves
withwiththe onedimensional
spin
Ge
∼2.82
meV
the Hanle-eﬀectcurvesthe one
spin
Geof
∼2.82
meV [41].
[41].
Y. dimensional
Fujita et al., Phys.
Rev. Applied
8,of014007(2017).
3
CFASτ (High-RA)
drift diﬀusion
model[32],whichwhichis expressed
as follows.
Takingintoaccount
the temperaturetemperatureindependent
independentdrift
diﬀusionmodel[32],isexpressedasfollows.
Takingintoaccounttheτs , s ,One dimensional spin drift diffusion model" " # # wewecan! ∞! ∞
CFAS(Low-RA)
interpret
the
decay
of
the
spin
signals
in
Fig.
2(a)
can interpret the decay of the spin signals in Fig. 2(a)Pinj Pdet
ρGe
λGe
t t
Pinj
Pdet
ρGe λDGe∆RNL (B=(Bz ) =φ(t)cos(ω−−dt,dt,
CFAS/CF
asasa aconsequenceof thethe reduction
reduction
P
and
P det
with indicates that there is almost∆R
φ(t)cos(ωconsequence
ininPthis
and
P det
with
0.2
z )NL
L t)exp
L t)exp
injinj± 0.01µm.
Theobserved
weak
temperaturedependence[23]. As
study
clearlySSτs τs increasing
00~ 0.2 nsincreasingtemperature.
temperature. Surely,
of of
(P(P
Surely,thethevaluevalue
inj ×Pdet )det )inj ×P"#"#of λGe± 0.01 µm at =125
K areinconnotocontributionofτNotephon to τs in Fig. 3(b), we can under1 andd2λGe
d2 = 0.52
1∼0.0004
at
8
K
was
down
∼0.0001
at
125
K.
=∼0.0004
at
8
K
was
down
to
∼0.0001
at
125
K.
Note
τ
:
Spin
lifetime(RT)
D: Diffusion constant√ exp withexp
√ =φ(t) =φ(t)− −the expected(2)(2)that
sistent
temperaturedependence
anditsstand τsdependence
withinrange
of 8 K ≤100
T ≤ 125 150
K as a resulttheττs s value
value andandthis
0 a in
50
200
250
the
its temperaturetemperaturedependence
in this
4πDt 4πDt 4Dt 4Dt ω = gµB /ħ: Larmor frequency (g = 1.56) thatstudyarearelargely
largely
diﬀerent from
those
inin
Ref.
[22][22]
despiteλGe B∼ /!
1.3 µm
at 130frequency,
K in Ref.[22].
Fromthe
λGe valueof onlythedonor-induced
diﬀerent
from
those
Ref.
despite spin relaxation mechanism, as
whereω L = gµ
the Larmor
is the study+
B isz theis Larmor
T (K) the experwhere ωfrequency,g isgalso
the
the
use
ofnnusingwithalmost
the
same
donor
con-con+ -Ge layers
L = gµB B
z /!each
F. J. canJedemaet al., clarify
Nature410,
345of(2001).
fortemperature,
we
τ
by
the
theoretically
predicted
in Ref. [23]. Actually,
the
use
-Ge
layerswithalmost
the
same
donor
s
g-factor (g = 1.56)[34], µ√is the Bohr magneton.
centration. According to Ref. [23], even the experimentelectronelectron
g-factor(g = 1.56)[34], µB is B
the
Bohr magneton.
According to Ref.
[23], eventhe experiment
relation,= Dτ
is thecentration.
diﬀusionconstant.
data
consistent
The solid curvein Fig. λ1(c)a representative
Ge shows
s , where Dresult
Y. Fujita, KH
et al., Phys. Rev. Applied 8, 014007 (2017).
from 130 to297 K (ϵF ! imental
kB T ) should
not inbe Fig.
consid-3(b) are approximately
The solid
curve in Fig.
1(c) showsa representative
result√from 130 to√297 Kwe(ϵF ! withkB T ) theshouldnot be considof the fittingwith Eq.(2).
The τ susedand Dvalues at 8 semiconductors,
Becausethiswork
degenerated
theoreticallycalculated
τ
value
of
∼0.12 ns
imp
ered by the T behavior. In addition, despite only fourof the K
fittingwith+ Eq.(2). The τ s and D values at 8
for+the n -Ge layer are estimated to be ∼464 ps and ered by the T behavior. In addition, despite only fourshouldestimate
Eq. (4)studies
in Ref.[39].
when
we assume
aB = 6.45 nm [2], n = 8.2 × 1018 cm−3 ,of the pureThespin current
transport
in n-Ge [19–22],
2
K for the-GeestimatedD
to valuesbe ∼464fromps and
∼9.0n cm/s.layerThe τares and λGe values for each temperature studies of the pure spin current transport in n-Ge [19–22],2
the experimental methods for analyzing τs were scattered

Spin relaxation in n-Ge

τGe (ns)

ΔRNL (mΩ)ΔRNL (mΩ)

Highly spin polarized Co FeAl Si

ΔRNL (mΩ)ΔRNL (mΩ)

0

I = -1.0 mA
d = 0.4 µm

ΔRNL (mΩ)

20

20

s

L

z

Spin relaxation in Ge at room temp.

Room temperature spin transport in n-Ge

Spin lifetime

Spin diffusion length~ 0.25 ns *, **0.44 ± 0.02 µm **できる．一般的に，四端子非局所電圧測定で得られる｜ ∆RNL ｜は，|∆RNL | =!
"Pinj Pdet ρN λN
L
exp −
，
S
λN

n-Ge

(3.4)

(1018 ~ 1019 cm-3)で表される．ここで Pinj ，Pdet はそれぞれ強磁性電極で注入されるスピンと検出されるスピンのスピン偏極率である．これらの値を用いて定義される (Pinj × Pdet )1/2 は，スピン注入/検出効率と見なすできる．一般的に，四端子非局所電圧測定で得られる｜ ∆RNL ｜は，ことができる．ρN と λN はそれぞれ非磁性チャネルの抵抗率とスピン拡散長を表している．本実験!
"

Pinj Pdet ρN λN
S

LλN|∆RmΩcmexp −， λGe =
では，150 K での ρGe と λGe はそれぞれ 28.2
NL | = ，0.59 µm である．ここで，√Dτs である．

Optically detected spin lifetime?? is less than 1 ps??

p-Ge
(3.4)

(1017 ~ 1018 cm-3)

E. J. Loren et al., Phys. Rev. B 84, 214307 (2011).

ρN(ρGeL): Channel
S は Ge チャネルの断面積 (∼ 5.0 µm2 ) である．
は 1.0 resistivityµm である．これらの値を用いると(Pinj ×λN(λGe): Spin diffusion lengthで表される．ここで Pinj ，Pdet はそれぞれ強磁性電極で注入されるスピンと検出されるスピンのスピ
M. Johnson and R. H. Silsbee, Phys. Rev. B 37, 5312 (1988).
Spin
length 150 K における値であるが，この値はPdet )1/2 diffusionは ∼0.12 となる．これはZhou らが 4 K で Fe/MgO/Ge
ン偏極率である．これらの値を用いて定義される (Pinj × Pdet )1/2 は，スピン注入/検出効率と見なす[10]
λ (n-Ge)(at(0.0023)
RT) ~よりもおよそ二桁増大している
420 nm系で得た値．従って，
Ge チャネルでさえL21 -Co2 FeSi
Spin
diffusion
lengthことができる．
SpinlifetimeρN と λN はそれぞれ非磁性チャネルの抵抗率とスピン拡散長を表している．本実験

電極は，チャネル中のスピン蓄積を増大させることを可能にすることを実証できた．
λ (n-Ge) (at RT) ~ 460 nm

τ (n-Ge)(at150RT)~ 0.25nsλGe はそれぞれ 28.2 mΩcm，0.59 µm である．ここで，λGe =
では，
K での
ρGe と
ΔRNL (mΩ)-80
電極は，チャネル中のスピン蓄積を増大させることを可能にすることを実証できた．
-100

Ge channel

20
0

-80
ΔRNL

-100

Gate

-1000

-500

-60
S. Sugahara and M. Tanaka, APL (2004).

(b) -400
60
40

Ge
0
By (Oe)

p-Ge
500

1000

Ge

Ferromagnet0
Bz (Oe)400

Ferromagnet

20(a)150 K における非局所磁気抵抗曲線．
(b) 平行，および反平行磁化配置時の 150 K で観測された Hanle 効果曲線．

ΔRNL (mΩ)

図 3.12Ferromagnet

Ferromagnet

-60

Fe3Si

1000

-40

-20
-40

500

ΔRNL
0
Fabrication of p-Ge on
Heusler alloys
for-20
vertical-type spin MOSFET

-40
-60

MBE of p-Ge on a Heusler alloy

55

-400

0
Bz (Oe)4000.565 nmGate

ΔRNL (mΩ)

400By (Oe)~ 10 nmΔRNL (mΩ)

60

Ferromagnet-20

0.565 nm

0-500

-1000

(b)

Suggestion of a vertical device for p-Ge

Vertical-type spin transistors(a)Ferromagnet**M. Yamada, KH et al., Appl. Phys. Express 10, 093001 (2017).

√

Dτs である．
(a)
M. Yamada, KH et al., Applied Physics Express 10, 093001 (2017).
2
0
S は Ge チャネルの断面積 (∼ 5.0 µm ) である．L は 1.0 µm である．これらの値を用いると (Pinj ×-20
Pdet )1/2 は ∼0.12 となる．これは 150 K における値であるが，この値は Zhou らが 4 K で Fe/MgO/Ge-40[10]系で得た値 (0.0023) よりもおよそ二桁増大している．従って，Ge チャネルでさえ L21 -Co2 FeSi
-60

Suggestion of a vertical device for p-Ge

*Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).

Suggestion of a vertical device for p-Ge

Suggestion of a vertical device for p-Ge

D03-Fe3Si
Fe

D03-Fe3SiSi① Si-terminated Fe3Si

Ge(111) sub.

Ge(111) sub.

ideal

Fe3Si
Si

①

Ge

②

② Ge layer

Fe3Si(111)Fe
K cell

Fe × 3Si

Si

Ge

K cell

K cellS. Yamada, KH et al., Cryst. Growth & Des. 12, 4703 (2012).

Suggestion of a vertical device for p-GeFe
K cellSiGe
K cell

K cellS. Yamada, KH et al., Cryst. Growth & Des. 12, 4703 (2012).

Suggestion of a vertical device for p-Ge

Thermoelectric measurements=> p-type semiconductor

Fe3Si

Fe3Si

Fe3Si
p-Ge

p-Ge

p-Ge

Fe3Si

p-Ge

Fe3Si

Fe3Si

Fe3Si
Si(111) substrate
M. Kawano, KH et al., Appl. Phys. Lett. 102, 121908 (2013).

Epitaxial growth of p-Ge layers on Fe3Si

10 nm

Si(111) substrate

K. Hamaya et al., Mater. Trans. 57(6), 760 (2016).

Epitaxial growth of Fe3Si/p-Ge/Fe3Si on Si

Spin transport in p-Ge

Spin transport in CoFe/p-Ge/Fe3Si
IDC = 0.5 mA

Change to CoFe alloys

CoFe

I

10 K
SiO2

epi. Ge(p-type)dGe= 20 nm

Si(111)

10 K

H

S ~ 0.16 µm2

5 µm
10 nm
S. Sakai, KH et al., Semicond. Sci. Technol. 32, 094005 (2017).

I

IDC = 0.5 mA
50 K

SiO2

V

CoFe
Ge

dGe= 20 nm

Fe3Si

125 K

Si(111)10 mΩ

HRoom-temperature spin transport in p-Ge

M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

Spin relaxation in p-Ge

Spin transport in CoFe/p-Ge/Fe3Si

300 K

Ge
Fe3Si

Fe3Si

Si. sub.

V

CoFe

S ~ 0.16 µm2

5 µm

M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

± 0.01 µm. The observed weak temof λGe and λGe = 0.52 ± 0.01 µm
sistent with the expected tempera
A. Fert and H. Jaffres, Phys. Rev. B 64, 184420 (2001).
λGe ∼ 1.3 µm at 130 K in Ref.[22Opticalfor each temperature,
we can also√
C. Lange et al., PRB 85, 241303(R) (2012).
relation, λGe = Dτs , where D is
Because this work used degenerateshould estimate D values from Eq
estimated D as a function of temp
the Supplemental Material[29]. Uµe , in the inset of Fig. 3(a), we ca
0.3~ 0.4 ps
temperature,as(RT)
displayed in Fig.
function of temperature in previou
ted [19–22]. As stated in introdu
depend on n yet. Note that the omarkedlythanthose in pre
M. Kawano, KH
et al., Phys. Rev.smaller
Mater. 1, 034604(2017).
We can also extract the τs andting the Hanle-eﬀect curves with th

Spin relaxation in Ge at room temp.

n-Ge(1018 ~ 1019 cm-3)

Spin lifetime

Spin diffusion length~ 0.25 ns *, **0.44 ± 0.02 µm **Contents
1. Expectation for Ge spintronics
2. Crystal growth of Heusler alloys on Ge
3. Spin injection into n-Ge and p-Ge

p-Ge
(1017 ~ 1018 cm-3)

0.3 ~ 0.4 ps ***~ 30 nm ***4. For an enhancement in MR ratio*Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).
**M. Yamada, KH et al., Appl. Phys. Express 10, 093001 (2017).
***M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

Magnetoresistance in p-Ge devices
CoFe

0.02 % (at 10 K)

Magnetoresistance in p-Ge devices
Low spin polarization ?

CoFe

Issues of interface quality ?
epi. Ge(p-type)epi. Ge(p-type)Issues of Ge layers ?

Fe3Si

Fe3Si

MR (%) =Si. sub.

R ーR
R

Low spin polarization ?

x 100

10 nm
M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

Si. sub.

10 nm
M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

MR ratio in Ge spin devices
n-Ge

MR ratio in Ge spin devices

p-Ge

0.03 % (at 8 K)

0.02 % (at 10 K)

Spin lifetime

Spin diffusion length

MR ration-Ge~ 0.25 ns *, **0.44 ± 0.02 µm **0.03 %(at 8 K)p-Ge

0.3 ~ 0.4 ps ***~ 30 nm ***0.02 %(at 10 K)*Y. Fujita, KH et al., Phys. Rev. Applied 8, 014007 (2017).
**M. Yamada, KH et al., Appl. Phys. Express 10, 093001 (2017).
***M. Kawano, KH et al., Phys. Rev. Mater. 1, 034604 (2017).

Summary
1. We achieved room-temperature spin transport
in n-Ge and p-Ge.
2. Room-temperature Spin lifetime and spin diffusion length
were estimated reliably.
Y. Fujita, K. Hamaya et al., Phys. Rev. Applied 8, 014007 (2017).
M. Yamada, K. Hamaya et al., Appl. Phys. Express 10, 093001 (2017). (Spotlights)
M. Kawano, K. Hamaya et al., Phys. Rev. Mater. 1, 034604 (2017).

However, the observed MR ratio in Ge-based spin valves was
only 0.02~0.03 % even at low temperatures.

For an enhancement in the MR ratio in Ge devices, we need novel
suggestions of material evolution by computational science.