11

Th. Wichert1, J.Kronenberg1, K. Johnston1, J. Cieslak1, M. Deicher1, F. Wagner1, H. Wolf1, and The ISOLDE collaboration2

1Technische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany 2CERN, CH-1211 Geneva 23, Switzerland

thw@tech-phys.uni-sb.de

Supported by the BMBF, contract 05 KK7TS1

Uncovering New Diffusion Phenomena in Uncovering New Diffusion Phenomena in Compound SemiconductorsCompound Semiconductors

ISOLDE Workshop and Users Meeting 2009ISOLDE Workshop and Users Meeting 2009

2

0 100 200 300 400 500108

109

1010

1011

1012

1013

1014

conc

entr

atio

n (c

m-3)

depth (µm)

concentrationof dopants

2

Diffusion in Solids

one-sidedsource

monotonously decreasing profile

"for his work on the use of isotopes as tracers in the study of chemical processes"

George de Hevesy

Nobel Prize in Chemistry 1943

3

Fick‘s First Law

Jx = - D dC/dx

dC

dx

4

828K (60 min)

Cd atmosphere

4

Diffusion of 111Ag in CdTe

• no loss of activity• diffusion towards increasing Ag concentration

0 100 200 300 400 500108

109

1010

1011

1012

1013

1014

conc

entr

atio

n (c

m-3)

depth (µm)

550K (30 min)

vacuum

implanted profile

5

Jx = - D dC/dx

dC

dx

Fick‘s First Law

violated by the present data ?

„uphill“

6

Table of Content

Radiotracer Diffusion in Binary Semiconductors

- Semiconductors and uphill diffusion

- Uphill diffusion and self-interstitials

- Self-interstitials and metal layers

On-line Diffusion Chamber

Following the set-up by the Stuttgart group (T1/2 > 10 min):

7

Radiotracer Technique

a

CdxZn1-xTeØ = 6 mmd = 800 µm

Implantation

CdTethermal

treatment

550 … 900 K60 keV

Used isotopes :111Ag, 67Cu, 24Na, 43K, 56Mn, 59Mn(59Fe), 65Ni, 61Mn(61Co), 101Cd(101Pd), 191Hg(191Pt), 193Hg(193Au)

2 gm

1...30 µm

0 100 200 300 400

1011

1012

1013

1014

depth (µm)co

nce

ntr

atio

n (

cm-3

)

CdTe:111Ag

Tdiff = 570 K tdiff = 30 min

DAg = 7.6·10-9 cm2/s

30nm

111Ag+

88 8

0 200 400 6001011

1012

1013

1014

0 200 400 600

1011

1012

1013

0 200 400 600108

109

1010

1011

0 200 400 600109

1010

1011

1012

828 K

con

cen

tra

tion

(cm

-3)

111Ag 67Cu 800 K

24Na 750 K

con

cen

tra

tion

(cm

-3)

depth (m)

193Au 800 K

depth (m)

t = 0:-layer at x = 0

profile symmetry:

dopant in equilibriumwith host crystal

profile shape:

result ofintrinsic defects

Uphill-diffusion

CdTeTe-saturated CdTe: tdiff = 60 min, external Cd pressure

Experimental Results

999

C: deviation from stoichiometry

T-C phase diagram (sketch)

C = CTeInitial CdTe:

Cd Cd

CTe CCdCCd

external Cd pressure

Control of Intrinsic Defects

CdTe

101010

Te sublattice: „perfect“

Cd sublattice

donors

acceptors

intrinsic extrinsic

i Cd CdC Cd V Ag

Defects Involved

… and all defects can be charged

=> Deviation from stoichiometry

111111

Fick‘s First Law revised

Particle Flux J

xJ D Cxusually C : concentration

(1 species)

in general µ : chemical potentials (several species)

xJ Lx

121212

AgAg

Ag

Ag

Cd

CdCd

Cd

F

FF

F

µ

µCq µ

C

µ

C C CC µ

µ

Ag Ag Ag

µµAg

q C

µ

µ

q

d d

q C

µµ

Fick‘s First Law revised

Changein the

concentrationsof

Ag atomsintrinsic defectscharge carriers

driven by thechemical potentials

1313

Modelling of Experimental Results

interaction of dopants with intrinsic defects

charge states of extrinsic and intrinsic defects

profile of C leads to formation of p/n junctions

drift in internal electric field

H. Wolf et al., Physica B 308-310 (2001) 963H. Wolf et al., Physica B, 340 - 342 (2003) 275 - 279H. Wolf et al., Phys. Rev. Lett. 94 (2005) 125901.H. Wolf et al., Defect and Diffusion Forum 237-240 (2005) 491.F. Wagner et al., Proc. of the 1st Int. Conf. on Diffusion in Solids and Liquids (DSL 2005)H. Wolf et al., J. Electr. Mater. 35 (2006) 1350.F. Wagner et al., Physica B: Condensed Matter 401-402 (2007) 286-290H. Wolf et al., Diffusion Fundamentals 8 (2008) 3.1-3.8F. Wagner, Dissertation, Universität des Saarlandes (2008)H. Wolf et al., Defect and Diffusion Forum Vols. 289-292 (2009) 587-592

14

0 200 400 600 800

1011

1012

1013

-4x1016

-3x1016

-2x1016

-1x1016

01x10

162x10

16

conc

entr

atio

n (

cm-3)

depth (µm)

[ ΔC

] (cm

-3)

-0,2

-0,1

0,0

0,1

µ F e

V

[ΔCini]

VCd

--Cd

i

++Cd

i

++n np

[ΔC] = [Cdi] - [VCd]

CdTe is Te-rich [ΔC] < 0

• [ΔC] determines µF

• Cd-atmosphere: Ag - diffusion

• [Ag] = [Agi+] highly mobile

• Agi+ behaves like h+

• Ag profile reflects µF and [ΔC]

Cdi Cdi

Profile Simulation

111Ag → CdTe

828 K(60 min)

1515

0 200 400 6001011

1012

1013

1014

0 200 400 600

1011

1012

1013

0 200 400 600108

109

1010

1011

0 200 400 600109

1010

1011

1012

828 K

conc

entr

atio

n (c

m-3)

111Ag 67Cu 800 K

24Na 750 K

conc

entr

atio

n (c

m-3)

depth (m)

193Au 800 K

depth (m)

C > 0n-type C < 0

p-type

C > 0n-type

D(Cdi) = 1.210-6 cm2/s

Experiment and Simulation

information about: diffusion coefficients formation energies ionizations energies

1616

0 200 400 6001011

1012

1013

1014

0 200 400 600

1011

1012

1013

0 200 400 600108

109

1010

1011

0 200 400 600109

1010

1011

1012

828 K

conc

entr

atio

n (c

m-3)

111Ag 67Cu 800 K

24Na 750 K

conc

entr

atio

n (c

m-3)

depth (m)

193Au 800 K

depth (m)

C > 0n-type C < 0

p-type

C > 0n-type

D(Cdi) = 1.210-6 cm2/s D(Cdi) = 7.010-7 cm2/s

D(Cdi) = 4.010-7 cm2/s D(Cdi) = 1.510-7 cm2/s

D(Cdi) should

not depend on

the dopant!

Experiment and Simulation

1717

0 200 400 600 800109

1010

1011

1012

1013

conc

entr

atio

n (c

m-3)

depth (µm)

0 200 400108

109

1010

1011

1012

1013

1014

conc

entr

atio

n (c

m-3)

depth (µm)

0 200 400 600 800

1011

1012

1013

conc

entr

atio

n (c

m-3)

depth (µm)

CdTe Cd0.96Zn0.04Te ZnTe828K, 60 min 828K, 60 min 928K, 24 h

comparable behavior in different II-VI semiconductors

Cd atmosphere Cd atmosphere Zn atmosphere

Ag in Different Semiconductors

104

18

Uphill Diffusion Profiles in Cd1-xZnxTe

18

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Matrix Isotope

0 200 400 600 800

1011

1012

1013

Kon

zent

ratio

n (c

m-3)

Tiefe (m)

peak

n p

19

Box shaped profiles in Cd0.97Zn0.03Te

19

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Matrix Isotope

0 100 200 300 400 5001010

1011

1012

1013

1014

30 min: vacuum 60 min: Cd atmosphere

conc

entr

atio

n (c

m-3)

depth (µm)

box

n p

2020

Influence of Metal Layers

111Ag in CdTe

Te-saturated (∆Cini = ∆C Te)

0 200 400 6001010

1011

1012

1013

1014

depth (µm)

D = 1.5·10-8 cm2/s

Tdiff = 500 K

co

nce

ntr

atio

n (

cm-3)

plus coppermetal layer

ΔCTeΔCCd

2121

Te-saturated (∆Cini = ∆C Te)

Influence of Metal Layers

111Ag in CdTe

0 200 400 6001010

1011

1012

1013

1014

depth (µm)

D = 1.5·10-8 cm2/s

Tdiff = 500 K

Tdiff = 580 K

Cu layer

co

nce

ntra

tion

(cm

-3)

plus coppermetal layer

ΔCTeΔCCd

2222

0 200 400 6001010

1011

1012

1013

1014

Tdiff

= 500 K

Tdiff

= 580 K

Cu layer

con

cent

ratio

n (

cm-3)

depth (µm)

Cd-saturated (∆Cini = ∆CCd )

Influence of Metal Layers

111Ag in CdTe

23

0 200 400 600 8001010

1011

1012

1013

1014

1015

1016

Cu Ni Au Al

conc

entr

atio

n (c

m-3)

depth (µm)

Influence of Metal Layers

111Ag in CdTe ( 580 K )

Te-saturated (∆Cini = ∆C Te)

24

0 200 400 600 8001010

1011

1012

1013

1014

1015

1016

Cu Ni Au Al

conc

entr

atio

n (c

m-3)

depth (µm)

Influence of Metal Layers

111Ag in CdTe ( 580 K )

Te-saturated (∆Cini = ∆C Te)

25

0 200 400 600 8001010

1011

1012

1013

1014

1015

1016

Cu Ni Au Al

conc

entr

atio

n (c

m-3)

depth (µm)

Influence of Metal Layers

111Ag in CdTe ( 580 K )

Te-saturated (∆Cini = ∆C Te)

26

0 200 400 600 8001010

1011

1012

1013

1014

1015

1016

Cu Ni Au Al

conc

entr

atio

n (c

m-3)

depth (µm)

Influence of Metal Layers

111Ag in CdTe ( 580 K )

Te-saturated (∆Cini = ∆C Te)

27

0 200 400 600 800

1011

1012

1013

conc

entr

atio

n (c

m-3)

depth (µm)

Uphill Diffusion

Cdi Cdi

ΔCTe ΔCCdΔCCd

evaporatedmetal

ΔCTeΔCCd

0 200 400 600 8001010

1011

1012

1013

1014

1015

1016

Cu Ni Au Al

conc

entr

atio

n (c

m-3)

depth (µm)

external Cd vapour pressure(symmetric Ag profile)

metal layer evaporated on surface (asymmetric Ag profile)

Injection of Cd Interstitials by

28

0 200 400 600 800109

1010

1011

1012

1013

1014

conc

entr

atio

n (c

m-3)

depth (µm)

0 200 400 600 800

1011

1012

1013

conc

entr

atio

n (c

m-3)

depth (µm)

evaporatedmetal

ΔCTe ΔCCdΔCCd

Cdi Cdi

ΔCTe ΔCCdΔCCd

at 800 K at 550 Kexternal Cd vapour pressure

(symmetric Ag profile)

Uphill Diffusion

29

• Catcher and tape-station• Germanium-detector + “PET”• Sample depot• Remote control (radioprotection)

Isotope T1/2 Detection

38Cl 37,3 min β-4800keV ; γ2168keV

11C 20,38 min β+ ; γ511keV

13N 9,96 min β+ ; γ511keV

29Al 6,6 min γ1273keV

(15O) 122 s β+ ; γ511keV

Sputter-sourceSputter-sourceCatcher, Tape station, DetectorCatcher, Tape station, Detector

BeamportBeamportDepotDepot

FurnaceFurnace ManipulatorManipulator

29

1) Open beamline2) Depot3) Implantation4) Annealing5) Sputtering

ManipulatorManipulator

On-line Diffusion Chamber

30

FurnaceFurnace

Sputter-sourceSputter-source

Tape stationTape station

BeamportBeamport

30

ManipulatorManipulatorD

etec

tor

Det

ecto

r

On-line Diffusion Chamber

31

Summary

1. Diffusion experiments in binary semiconductors

Importance of radioactive isotopes at ISOLDE :elements, implantation, purity.

2. Observation and understanding of unusual diffusion profiles

General formulation of Fick‘s law :uphill diffusion, quantitativ understanding, metal layers.

3. On-line diffusion chamber for short-lived isotopes

Access to well-needed light elements.

0 200 400 600 800

1011

1012

1013

Kon

zent

ratio

n (c

m-3)

Tiefe (m)

peak

n p

0 200 400 6001010

1011

1012

1013

1014

depth (µm)

D = 1.5·10-8 cm2/s

Tdiff = 500 K

Tdiff = 580 K

Cu layer

co

nce

ntr

atio

n (

cm-3)

Cu layer

w/o layer

Uni Münster:

H. MehrerN.A. StolwijkH. BrachtA. Rodriguez Schachtrup

Uni Bonn:

R. ViandenD. Eversheim

CERN:

ISOLDE Collaboration

BMBF for financial support

Uni Prague:

R. GrillE. Belas

Thanks to …

… you for your attention

33

Summary

1. Diffusion experiments in binary semiconductors

Importance of radioactive isotopes at ISOLDE :elements, implantation, purity.

2. Observation and understanding of unusual diffusion profiles

General formulation of Fick‘s law :uphill diffusion, quantitativ understanding, metal layers.

3. On-line diffusion chamber for short-lived isotopes

Access to well-needed light elements.

0 200 400 600 800

1011

1012

1013

Kon

zent

ratio

n (c

m-3)

Tiefe (m)

peak

n p

0 200 400 6001010

1011

1012

1013

1014

depth (µm)

D = 1.5·10-8 cm2/s

Tdiff = 500 K

Tdiff = 580 K

Cu layer

co

nce

ntr

atio

n (

cm-3)

Cu layer

w/o layer

34

36

Future : Short Lived Isotopes

36

Isotope T1/2

38Cl 37,3 min11C 20,38 min13N 9,96 min29Al 6,6 min

(15O) 122 s

Diffusion of C, N and O in semiconductors Self-diffusion in Al and in Al alloys Diffusion of C, N, and O in grain boundaries of nanomaterials

Following the set-up by the Stuttgart group (T1/2 > 10 min):

On-line diffusion chamber

3737

0 200 400 600

1x1011

1x1012

1x1013

1x1014

Tdiff = 729 K

60 min

con

cen

tra

tion

(cm

-3)

depth (µm)

CdTe:111Ag

x

1.0 1.5 2.0 2.5 3.01.5

2.0

2.5

1000100

tdiff (min)

log

(x/

µm

)log(tdiff/min)

10

1.0 1.5 2.0 2.5 3.01.5

2.0

2.5

1000100

tdiff (min)

log

(x/

µm

)

log(tdiff/min)

10

diffx t

dissolution ofprecipitates ...

... takeninto account

profile analysis

effective D(Cdi) depends on

● density and size● dissolution rate

of precipitates

taking into accountdissolution of precipitates:

quantitative descriptionof x(tdiff)

model predicts:

diffx t

used samples:

different with respectto precipitates

383838

Defect interactions

in local equilibrium:

charge states of defects:

Cdi0, Cdi

+, Cdi2+

VCd0, VCd

-, VCd2-

Agi0, Agi

+

AgCd0, AgCd

-

e-, h+

donor

acceptor

donor

acceptor

}}

intrinsic (6)

extrinsic (4)

free carriers (2)

defect concentration:

0B B

F(Y) (Y)Y C exp exp

k T k T

C0: number of available lattice sites

Three chemical

potentials

Three corresponding

concentration quantities

defects taken into account

393939

diffusion equations

unchanged upon

defect reactions

i CdAg Ag Ag

i Cd CdC Cd V Ag

2Cd Cd Cd

2i i i

Cq 2 V V Ag e

2 Cd Cd Ag h

i

i CdCd i

2 2

20

Ag i

q

V C

A

q

d

d d d

dt dx dxd d d

dt dx dx

e d

dx

DC

Ag D Ag

C

Cd D V

qAA

A qq

qA

µ

µCq µ

Cq Cq

µ

C

Ag Ag Ag

µAg µ

C CC µ

µ

µ

d d

Cq

µ

µ

µ

AgCd is regarded as not mobile

µA := µ(Agi0)

µ := µ(Cdi0)

µq := µ(e-)

4040

profile analysis

Ag dopant mostly incorporated as Agi

+

pn-transitions formedin front of penetrating

Cdi defects

Ag dopant inequilibrium with

host crystal

chemical potentialscharge density and

stoichiometry deviationincorporation sites

of Ag dopant

essentially the same results for Cu, Au, and Na dopant

0 200 400 600 800-1.0

-0.5

0.0

0.5

µ + 2 eV

µA + 1 eV

depth (µm)

ener

gy (

eV)

µq

0 200 400 600 800-1.0x1017

-5.0x1016

0.0

5.0x1016

1.0x1017

-1.0x1011

-5.0x1010

0.0

5.0x1010

1.0x1011

[C]

depth (µm)

con

cen

tra

tion

(cm

-3)

[Cq]

0 200 400 600 800109

1010

1011

1012

1013

[Ag0Cd]

[Ag-Cd]

[Ag0i ]

depth (µm)

co

nce

ntr

atio

n (

cm-3)

[Ag+i ]

414141

AgAg

Ag

Ag

Cd

CdCd

Cd

F

FF

F

µ

µCq µ

C

µ

C C CC µ

µ

Ag Ag Ag

µµAg

q C

µ

µ

q

d d

q C

µµ

424242

i CdCd i V Cd

Cd C

F

F dF

Cq

Cq CD D Cd

qD V

C C

2 2i i Cd Cd

2 2i i Cd Cd

Cd i Cd

CdF

F

2 Cd

C Cd V

Cd 2 V V

Cq 4 Cd Cd h 4 V V e

CqC

2 2Cd Cd i i2 V V e 2 CC d h 0q Cd

434343

Cu-layer CdTe

Cd-layer acting asstrong source for

intrinsic defects (Cdi)

CdTeCu-layer

Cu-Tealloy

550 K

2-3 ML Cd at the interface would be sufficient !

Cu and Au layer on surface

4444

t1/2 > 2 d 1 h < t1/2 < 2 dcurrent

t1/2 < 1 hfuture/current

Plasma ion sourceSurface ionization (+/-)Laser ionization

600 isotopes, 68 elements600 isotopes, 68 elements

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Ag

Ia

IIa

IIIb IVb Vb VIb VIIb VIII Ib IIb

IIIa IVa Va VIa VIIa

VIII

Zn

Cd In

N

Sb

S

Se

Te

Cl

Br

I

As33

15

7

H

Be

Mg

Ca Sc Ti

Sr Y

V Cr Mn

Zr Nb Mo Tc

Fe Co Ni

Ru Rh Pd

B

Al

Ga

C

Si

Ge

Sn

P

O F

He

Ne

Ar

Kr

Xe

Cu

4

12

20 21 22 23 24 25 26 27 28 29 30 31

13

5

32

14

6

34

16

8

35

17

9

36

18

10

2

38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54

Li

Rb

Na

K

1

3

11

19

37

Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83

Cs55

Radioactive Tracers

600 isotopes, 68 elements