Artificial Atoms
in Semiconductors

a t e ri alsesteDev

ic

SPINTECH 6Matsue, JapanmsM

Paul Koenraad
Department of Applied Physics
Eindhoven University of Technology

Sys

COBRA Inter-University ResearchInstitute on Communication Technology

2 August 2011

Atomic States Hydrogen!2 k 2 " !2!2!2 %1H! =++!
+! = "!
222'$2m # !x!y!z &" or
l=0
m=0

l=1
m=0 m=1

l=2
m=0 m=1

m=2

n=3
n=2! Ryd! n,l,m = ! 2n! n,l,m = Rn (r / a0 )Yl,m (" , # )n=1
http://www.orbitals.com/orb/index.html

Rydberg energy

me 4! Ryd = ! 2 2 = !13.6 eV
8h ! oBohr radius

4!" 0 ! 2a0 == 0.053 nm
2me

Ground state wavefunction! (1s1/2 ) = 2 / 4! (1/ rB ) e
3/2!r / rB

n=1

n=2

l=0
m=0
l=1
m=0
l=1
m=1

Effective Bohr-radiusrB =εr
m*

l=2
m=0

a0

Ground state binding energyε=m*εr2ε Rydn=3

In GaAs εr = 13 and m* = 0.067
ground state binding energy ε0 = 5.6 meV
and the effective Bohr radius rB = 10 nml=2m=1

l=2m=2

http://www.orbitals.com/orb/index.html

HydrogenicImpurity in aSemiconductorHydrogenic Atoms in Semiconductors
Questions:1) what is the effect of the surface on
the electronic and spin properties?

STM tip2) What happens for non-hydrogenic
like impurities?
vacuumsemiconductor

In top surface layer

Binding energy
E(meV)
[meV]
donor

87
65

Near surface

43

See for instanceG. Bastard, PRB 24, 4714 (1981)

210102030

Depth [nm]40

Depth below surface (nm)50

Deep in the bulk

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Cross-sectional STM

Wafer

Cutting out a sample

Clamping the sample

STM TipGrowthdirection

UHV (10-11 torr)

In situ cleaving the sample

Assessment at the Atomic Scale

9 nm * 8 nm

InAs self-assembled
quantum dot in InGaAs

Two Si impurities in GaAs

110-surface
cleaved III/Vsample

UHV (10-11 torr)

GaAs dot in
AlGaAs grown by
Ga droplet
techniqueGrown by T. Mano,Tsukuba, Japan

J.G.Keizer, J.G. et al,
APL 96, 062101 (2010).

Scanning Tunneling Microscopy
on Semiconductors
Iz
Ec
EF
EvEF
eV

Egap
EFEv

eV
EF

sampletiptipEC

VsampleScanning Tunneling Microscopy
on Semiconductors
Positive sample voltage

Negative sample voltage(empty states)(filled states)

zz

Ec
EF
Ev

EF
eV

Egap

sample

tip

Ec
EF
Ev

Egap
EF
sampleDepletion, accumulation, inversion

tipeV

45 nm * 35 nm

Bulk doped Mn:GaAs

Celebi et al PRL 104, 086404 (2010)

Mn Substitution in a GaAs Surface

D. Kitchen et al, Nature 442, 436 (2006)

Artificial Atomsin Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Low Temperature Imaging
Si Doped GaAs measured at 5 K
tip

50 nm * 50 nm

VacuumSi donors at different depths
below the 110 cleavage surface

Low Temperature Imaging

8 nm * 8 nm

50 nm * 50 nm

Si Doped GaAs measured at 5 K

Si donors at different depths
below the 110 cleavage surface

Single Si donor in GaAs

Ionization process
topography:AB

12 x 12 nm

CSi+

ASi0B

C

tip
zx,y+

K. Teichman et al, PRL 101,076103 (2008)

sampleIonization process

dI/dV topography:

ASi0B

differential conductivity:C

2.5
sample voltage (V)12 x 12 nm

Si+

B
A

tip

Czx,y+
sampleSi0Si+

AB C

21.5

1-5

-2.5
02.5
lateral position (nm)K. Teichman et al, PRL 101,076103 (2008)

5Voltage Dependence
R. M. Feenstra, J.Vac. Sci. Technol B 21, 2080 (2003)

flat band voltage and tip radius are
the main fitting parameters

Ionization rings for Mn in InAs
dI/dV map at 1.05 VdI/dV map at 1.10 V

F. Marczinowski et al, PRB 77, 115318 (2008)

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Potentiometer
The shift !V (r)in the I(V)spectra corresponds withthe local potential

I1V1

topography:

current (pA)

600

free surface
above donor

400!V!V200
00

I20.5

1
1.5
voltage (V)

22.5

V2

Coulomb Potential ofa near surface Donor
11
V=4!" 0" r (x 2 + z 2 )1/2

D+zx

DV in eV00.1

fit: z = 0.4 nm ! r= 8
0.2

0.3-4-3-2-1

K. Teichman et al, PRL 101, 076103 (2008)

0x in nm1234

Coulomb Profiling with an As-vacancy

STM induced creation ofAs-vacancy near Mn in GaAs

D. Lee and J. Gupta, NanoLetters 11, 2004 (2011)

Coulomb Profiling with an As-vacancy
As-vacancy at surface is a singly charged donor

εr = 7

D. Lee and J. Gupta, NanoLetters 11, 2004 (2011)

Coulomb Interaction(0,+)

D2(+,+)

(+,0)

D1
(0,0)

(D1,D2) = charge state donor pair
K. Teichman et al, submitted for publication

Depth Dependent Binding Energy

A.P. Wijnheijmer et al PRL 102, 166101 (2009)

Depth Dependent Binding Energy	  3020	  Binding energy (meV)

40

10Ed,bulk = 5.6 meV

00,00,40,8Depth (nm)A.P. Wijnheijmer et al PRL 102, 166101 (2009)

1,2

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Switching of Si in the Surface Layer
0.8 V

1.0 V

D+D00.7 VD-Topographic heigt (pm)

J. Garleff et al,in press PRB

D+50

0D-50

048Lateral position (nm)

Bond Reconfiguration
D-D0

Substitutionalposition

Interstitialpositiond++e“ DX- “D0D+D-

Only observed for Si donors in
the topmost layer

P. Mooney, Semi. Sci & Technol. 6, B1 (1991)

Si+ / Si- - Switching Rate	  4 ,0Temperature dependence

3 ,52 ,5

#E &! !1 = " 0 + " " exp % B ($ kT '2 ,01 ,5	  Switching rate (Hz)3 ,0EB = (12 ± 5) meV

1 ,0configuration coordinate

0 ,50 ,00

102030Temperature (K)4050

J. Garleff et al, in press PRB

Impurity ModelAs

Ga

Hydrogenic donor (Bright)

DX -(Dark)

Increasing
tip voltage
configuration coordinate

J. Garleff et al, in press PRB

configuration coordinate

Artificial Atoms
in SemiconductorsOutline
üIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulationüMagnetic characterization
üConclusionsElectronic Structure
magnetic doping: a part of the atoms
in the crystal is replaced by magnetictransition metal impurities
4sp	 4sp	 4sp	 4sp

Ga-atom GaAs
3d	

3d	

3d	

3d	3d	

Mn on Ga-site in GaAs
Mn-atom GaAs

4sp	 4sp	 4sp	-(3d5+h)+p-d interaction results inanti-ferromagnetic alignment

3d	

3d	

3d	3d	3d	Manipulation of theCharge State by an STM tip
Ionized donor

Neutral donor

Ec

Negativesamplevoltage

EFEvn-typesample

EcD0Evtip

Positivesamplevoltage

D+EFn-typesampletip

Manipulation of theCharge State by STM tip
Neutral acceptor

Ionized acceptor

EcEv

Negativesamplevoltage

EFp-type
sampleEcA–Evtip

Positivesamplevoltage
A0EFp-typesampletip

Neutral Mn Ao (ion + hole)(V=-0.9 V)(V=+0.7 V)

14 nm * 14 nm

Ionized Mn A–[110][001]

Contrast is due to Coulomb field

Tunneling to the bound hole
(Mn in ~ 3rd sublayer)

5.6 nm * 5.6 nm

A– and Ao Charge States of Mn

110-plane
J=1/2

Luttinger Hamiltonianεe

J=3/2

H Lut (k x , k y , kz )! i + V (r)! i = " i! iεhh (mJ=3/2)
εlh (mJ=1/2)"Luttinger Hamiltonian $ H hh+!2 $ c
H Lut (k x , k y , kz ) =$2mo $ !b +$ 0$#c!bH lh

00H lhb+c+%'b ''c 'H hh ''&0()
H = ( k + k ) (! ! ! ) + k (! + 2! )H hh = k x2 + k y2 (! 1 + ! 2 ) + kz2 (! 1 ! 2! 2 )lh2x2y122z

1b = 2 3! 3 (k x ! ik y )kz()

c = ! 3 "#! 2 k x2 ! k y2 ! 2i! 3k x k y $%# " ! 3 / 2, +3 / 2
1%% "2 ! 3 / 2, +1 / 2!i = %% "3 ! 3 / 2, "1 / 2% " ! 3 / 2, "3 / 2$ 4&((((('4-vector
representation
based onspin-projection

In confined systems the light andheavy hole bands are mixed

2γ1, γ2 and γ3
Luttinger
parameters

γ2 = γ3 isotropic dispersion

Modelling of Acceptors
Experimental

Cubic symmetry
selects d-states
contributing to theground stateenvelope with T2
symmetry_[110][001]TBM

Yakunin et al. PRL 92,216806 (2004)

EMM (envelope)

TBM (envelope)

A. Monakhov, Ioffe, Russia

J.-M. Tang and M. Flatté, Iowa, USee
EaelhehhMeasured at 5K

Mn Doped GaAs

Garleff et al PRB 78 075313 (2008)

Celebi et al PRL 104, 086404 (2010)

Kitchen et al., Nature442, 436 (2006)

Depth dependent contrast
Surface

123

4

5

6

Surface Mn

Celebi et al PRL 104,086404 (2010)
J. Garleff et al
PRB 78, 075313 (2008)

Strained Mn impurities
ExperimentTBM

A. Yakunin et al, Nature Materials 6, 512 (2007)

EFM

Effect of Surface relaxation
vacuumexpTBM
As_TBM*[110]Ga[001]
Ga sublattice shifted by0.014 Ang in 110 direction(0.25 % of lattice constant)Celebi et al PRL 104, 086404 (2010)

Mn Contrast
Kitchen et al., Nature442, 436 (2006)

ExpTheTheExp

The001

4th sublayer

surfaceExp

C. Celebi et al PRL
104, 086404 (2010)

J. Garleff et al PRB 78, 075313 (2008)

T.O. Strandberg et al.
PRB 80 024425 (2009)

Binding Energy Mn Acceptor

Theory: T.O. Strandberg et al.
PRB 80 024425 (2009)

J. Garleff et al PRB 82 035303 (2010)

Shallow versus
Deep Impurities
Shallow impurities- Long range confining potential mostly
Coulombic (1/r)- Effective mass modeling- Large Bohr-radius, small binding energy- Examples in GaAs: Si, Zn, Be, Sn

Deep impurities- Atomic scale confining potential
strongly non-Coulombic- Advanced atomistic modeling- Strongly localized, large binding energy
P. Mahadevan and A. Zunger APL 85, 2860 (2004)- Examples in GaAs: Fe, Cr, ErTransition Metal Impurities in GaAs

Half-filledd-shell

P. Vogl and J.M. Baranowski, Acta Physica Polinica A 67, 133 (1985)

Cr doped GaP
Empty state imaging

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusionsElectronic Structure Fe in GaAs
[Fe3+]0

Photo-excitation[Fe2+,h]03d	@ 480 meV
4sp	 4sp	 4sp	 4sp	

4sp	 4sp	 4sp	

3d	3d	3d	3d	Fe3+5

3d	3d	3d	3d	3d	Fe2+ + h(3d5)Isoelectric defect6(3d6+h)

Neutral acceptor

3d	Electronic Structure Fe in GaAs
[Fe3+]0

Photo-excitation[Fe2+]- + h+ 3d	> 510 meV
4sp	 4sp	 4sp	 4sp	

4sp	 4sp	 4sp	 4sp3d	3d	3d	

3d	Fe3+5

3d	3d	Fe2+(3d5)Isoelectric defect3d	3d	3d	+ Free hole

6

Neutral acceptor

(3d6)

3d	

Electronic Structure Fe in GaAs
EFermi[Fe3+]0Raise Fermi-level
EFermi4sp	 4sp	 4sp	 4sp	

3d	53d	3d	3d	(3d5)Isoelectric defect3d	[Fe2+]-3d	4sp	 4sp	 4sp	 4sp3d	3d	6

Neutral acceptor

3d	(3d6)

3d	3d	Charge Transfer Level Fe in III/Vacceptor[Fe2+]6CT-level[Fe3+]05

Isoelectric defectE. Malguth Phys. Stat. Sol. 245 455 (2008)

Charge state Fe depends on position Fermi level

Transition Metal Impurities in GaAs

EcEv

T. Graf, S. Goennenwein, M. Brandt, Phys Status Solidi B 239, 277 (2003)

Manipulation of theFe valence state[Fe3+]0 isoelectronic center[Fe2+]- charged acceptor
Negativesamplevoltage

Positivesamplevoltage

EcEcEFEvEF
CT-leveltip
At large negative voltage
ionized Fe2+

CT-levelEvtip
At large positive voltage
neutral Fe3+

Manipulation of Valence Stateof Fe by STM tip[Fe3+]0[Fe3+]0 iso-electronic dopantsp[Fe2+]-3d5[Fe2+]- ionized acceptor

POSTER Juanita Bocquel (FP-47)

sp3d6

-­‐1.9V	  -­‐1.3V	  -­‐1.5V	  -­‐1.2V	  -­‐1.4V	  -­‐1.1V	  Fe:GaAsInelastic tunnel effects involving d-state and the bound hole state of Fe2+ ??

Artificial Atoms
in Semiconductors
OutlineüIntroductionüAnalysis of individual donors in GaAs
üCharge manipulation (ionization)üElectronic characterization
üConfiguration manipulation (donor/acceptor)
üAnalysis of individual magnetic acceptors in GaAsüElectronic characterization
üValence state manipulation
üMagnetic characterization
üConclusions

Magnetic Field
Dependence[001][1-10]

[001]

[110]

[1-10]

0

1

2
[110]

[001]-[110]3Tang en Flatté, PRB 72, 161315(R) (2005)
T.O. Strandberg et al. PRB 80 024425 (2009)

Depth Dependence Mn ContrastEasy

Hard

Easy

Hard

Easy

Hard

1 below
surface4 below

7 below

2 below

5 below

8 below

3 below

6 below

T.O. Strandberg et al. PRB 80 024425 (2009)9 belowMagnetic Field Dependence
Mn acceptor deep below surface
B=(0,0,-­‐6)	  26 nm * 26 nm

B=(0,1,0)	  yz	  	  Temp ~ 2Ky	  x∆z=137.8	  pm	  	  B=(0,1,0)	  	  z	  	  ∆z=137.1pm	  x	  Magnetic Field Dependence
Mn acceptor deep below surface

Temp ~ 2K

0)

1)

2)

3)

4)

5)

6)7)

Magnetic
anisotropy asfunction of depth
below surface
Minimal energy
Low barrierHigh barrier

Magnetic
anisotropy

Depth in ML below Surface
Depth in ML below Surface

T.O. Strandberg et al, PRB 80 024425 (2009)

Spin Excitation of a Single Fe atom
in an InSb Top-Surface Layerinelasticelastic
A.A. Khajetoorians et al, Nature 467, 1084 (2010)

Spin Excitation of a Single Fe atom
in an InSb Top-Surface Layer(H = DŜ + E Ŝ ! Ŝ2z

D = 0.75 meV2x2y)E = 0.5 meVHard axis

inelasticelastic
A.A. Khajetoorians et al, Nature 467, 1084 (2010)

Anisotropic Spin-Interaction for
Mn in a GaAs Surface

Spectroscopic STM
measurements

D. Kitchen et al, Nature 442, 436 (2006)

Spin-Polarized Tunneling on Mn
Schlenhoff et al. APL 97, 083104 (2010)

Cr tipsPOSTER Joris Keizer (FP-26)

out-of-plane magnetization
observed on 1.5 ML Fe on W

Atomic resolution with Cr tip on Mn:GaAs

Collaborators
TU/e
J. Bocquel, M. Bozkurt, C. Celebi, J. Garleff, j. Keizer,
S. Mauger, A. Silov, A.Yakunin, I. Wijnheijmer
Experimental
S. Loth, K. Teichmann, M. Wenderoth, R.G. Ulbrich(University of Gottingen, Germany)
B. Bryant, N. Curzon, C. Hirjibehedin (UCL, London, UK)
TheoryM.E. Flatté, C.E. Prior (University of Iowa, USA)
J.M. Tang (University of New Hampshire, USA)
A. Monakhov, N. Averkiev (Ioffe-institute, Russia)
M. Roy, P. Maksym (University of Leicester, UK)
Growers
W. Van Roy (IMEC-Leuven, Belgium)
B. Gallagher, R. Campion, V. Grant, T. Foxon (Nottingham, UK)
E. Marega (San Carlos, Brazil) & G. Solomon (Arkansas, USA)

What did Pauli have to say
about semiconductor surfaces?
“One shouldn’t work on semiconductors,
that is a filthy mess; who knows whether
any semiconductors exist.”

What did Pauli have to say
about semiconductor surfaces?
“One shouldn’t work on semiconductors,
that is a filthy mess; who knows whether
any semiconductors exist.”

Review on single dopant physics and devices,
Nature Materials 10, 91 (2011)

What did Pauli have to say
about semiconductor surfaces?
“One shouldn’t work on semiconductors,
that is a filthy mess; who knows whether
any semiconductors exist.”

Review on single dopant physics and devices,
Nature Materials 10, 91 (2011)“God made the bulk; the surface was invented by the devil.”What did Pauli have to say
about semiconductor surfaces?
“One shouldn’t work on semiconductors,
that is a filthy mess; who knows whether
any semiconductors exist.”

Review on single dopant physics and devices,
Nature Materials 10, 91 (2011)“God made the bulk; the surface layer was invented by the devil.”Welcome in the Netherlands

PASPS-VII

Eindhoven
5-9 August 2012www.phys.tue.nl/PASPS1

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