Dietrich R. T. ZahnInstitut für Physik, Technische Universität Chemnitz, Germany

Surface Science with Optical Spectroscopies

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

SemiconductorSemiconductor PhysicsPhysics ––ActivitiesActivities in Chemnitzin Chemnitz

hω

ee

SemiconductorInterface

hω

Electrical Measurements:Current-Voltage (IV)Capacitance-Voltage (CV)(Deep Level) Transient Spectroscopy

Surface Science:Photoemission Spectroscopy(UPS and XPS)X-ray Absorption Fine Structure(NEXAFS)Auger Electron Spectroscopy(AES)Low Energy Electron Diffraction(LEED)Inverse PhotoemissionKelvin Probe (CPD)

Growth:(Organic) Molecular Beam Depositionin Ultra-High Vacuum(Metal-Organic) Vapour Phase Deposition

Optical Spectroscopy:Raman Spectroscopy (RS) PhotoluminescenceSpectroscopic Ellipsometry (SE) UV-visInfrared Spectroscopy (IR)Reflection Anisotropy Spectroscopy (RAS)

Information Depth

EU Funded Human Potential Research Training NetworkContract No. HPRN-CT-1999-00164, www.tu-chemnitz.de/diode

DDesigning esigning IInorganic/norganic/OOrganic rganic DEDEvicesvices

(v) The Overall Device Performance

GaAs(100)

Organic InterlayerMetal

V

I

(iv) The Interface betweenthe Organic Molecules and the Metal

(iii) The OrganicMolecular Film

(ii) The Interface betweenthe GaAs Substrate and the Organic Molecules

(i) The GaAs Substrate Surface

DDesigningesigning IInorganicnorganic//OOrganicrganic DEDEvicesvices

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

JuProf. Dr. Georgeta Salvan

hωs=hωi+hΩ

200 250 300 350

ZnSe LO

Intensity / ctsmW-1s-1

GaAs LO

Raman Shift / cm-1

1,5 2,0 2,5 3,0 3,51

10

100

1000

laser lines

Info

rmat

ion

dept

h / n

m

Photon energy / eV

Raman Spectroscopy

phis Ω±= hhh ωω

buried layers

surface

small focus

intensity∝ω4

high Eg materials

100 200 300 400 500 600 70050

100150

2002500.1

0.2

0.3

0.4 LOZnS LOZnSe+LOZnS

2 LOZnSeLOZnSe

Intensity / counts mW -1s -1

Temperature / °CRaman Shift / cm-1

with increasingtemperaturethe bandgapof ZnS0.05Se0.95approaches thephoton energyof 2.66 eV

typical gain oftwo orders ofmagnitude

Resonance enhancement

GaAs

Raman Spectroscopy combined with Molecular Beam Deposition

Molecular Beam Epitaxial Growth of ZnSe: Effect of Nitrogen Doping

Modulation due to Fabry-Perotinterference: Determination of growth rate and layer thickness

Identical experimental conditions, except: undoped doped

Incorporation of nitrogen causesbroadening of electronicresonance; plus compressivestrain in substrate

Desorption of a Se Capping Layer

Crystallisation during annealing

Temperature induced shift

Background due to roughness

Perylene derivativesPTCDA: 3,4,9,10- Perylenetetracarboxylic dianhydrideDiMe-PTCDI: 3,4,9,10- Perylenetetracarboxylic diImide

CC2424HH88OO66

y

x

z

CC2626HH1414OO44NN22

PTCDA Crystal

Experimentally derivedgeometry via X-ray analysis

3.21 Å

α - PTCDA β - PTCDAtwo molecules per unit cellα - and β - phases

bc b

c

Tsubstrate =295 K

PTCDA/S-GaAs(001):2x1 AFM Topography

Tsubstrate =410 K

Tsubstrate =360 K

PTCDA DiMe-PTCDI

Symmetry D2hRaman active: 19Ag+18B1g+10B2g+7B3g

IR active: +10B1u+18B2u+18B3u

Silent: + 8Au108 internal vibrations

Molecular Vibrational Properties

CC2424HH88OO66

• DiMe-PTCDI: Cambridge Structural Database.

• PTCDA: α- and β-phases: S. R. Forrest, Chem. Rev. 97 (1997), 1793.

Monoclinic crystallographic system in thin films:

CC2626HH1414OO44NN22

C2h44Ag+22Bg

+23Au+43Bu

+ 8Au132 internal vibrations

2-fold

DavydovSplitting

internal molecular modes: external molecular modes (phonons):

200 300 400 500 600 700

1200 1300 1400 1500 1600 1700

Inte

nsity

/ a.

u.

x2

Raman shift / cm-1

CC--OOBBgg

CC--HH CC--CC

CC--CC

SymmetrySymmetry: : DD2h2h CC2h2h (monoclinic)(monoclinic)

25 50 75 100 125 Raman shift / cm-1

Inte

nsity

/ a.

u. 6 rotationalvibrations:3Ag+3Bg

19Ag+18B1g+10B2g+7B3g

BBgg

AAgg

AAgg

BBgg

AAgg

RamanRaman--active vibrations of active vibrations of PTCDA PTCDA ((CC2424HH88OO66))::Effect of crystal formation Effect of crystal formation

200 400 600 12

Inte

nsity

/ ar

b. u

nits

Raman sh

Raman Spectra of a Raman Spectra of a PTCDAPTCDA CrystalCrystal

• assignment of modes and their relative atomic contribution using Gaussian `98 (B3LYP:3-21G).

Raman shift /cm-1

and a and a DiMeDiMe--PTCDIPTCDI

DiMe-PTCDI PTCDA

PTCDA DiMe-PTCDI

DiMe-PTCDI

PTCDA experimental

ω m= =0.97ω m

ω 221= =0.95ω 233

Raman Monitoring ofRaman Monitoring of PTCDAPTCDA Growth on Growth on SS--GaAs(100):2x1GaAs(100):2x1

200 250 300 350 400

LO Ω−

Nd = 2.7 *1018 cm-3

Ram

an in

teni

sty

/ a. u

.

Raman shift / cm-1

0 2 4 60.00.20.40.60.81.01.21.4

Raman PES

S-GaA

s

Ban

d B

endi

ng /

eV

Film Thickness / nm

PTCDA/S-GaAs

Electronic Properties at Electronic Properties at PTCDAPTCDA//SS--GaAsGaAs

• Relative intensities of GaAs LO and PLP (Ω-) bands:

Band bending within the substrate: minor changes upon PTCDA adsorption.

Good agreement with photoemission (PES) studies: S. Park, D.R.T. Zahn, et al. Appl. Phys. Lett. 76 (2000) 3200.

J. Geurts, Surf. Sci.

Rep. 18 (1993), 1.

4882

( 0)

GaAsn

nmdLO

n s

I eI

V z

δ

δ

−Ω

∝

∝ =

(a)

J. Luminescence, 110 (2004) 296

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

Gianina Gavrila

MUSTANG (Multi User STage for ANGularresolved photoemission) at BESSY

Mg / PTCDA / S-GaAs

537 534 531 528 525

Inte

nsity

/ cp

s*m

A-1

bare PTCDA

3.2nm Mg

1.6nm Mg

0.4nm Mg

Binding energy / eV

1 cp

s*m

A-1 0.1nm Mg

O1s core level MgO

292 290 288 286 284 282 280bare PTCDA

3.2nm Mg

1.6nm Mg

0.4nm Mg

Inte

nsity

/ cp

s*m

A-1

Binding energy / eV

4 cp

s*m

A-1

0.1nm Mg

C1s core level

54 53 52 51 50 49 48

3.2nm Mg

1.6nm Mg0.4nm Mg

Binding energy / eV

40 c

ps*m

A- 1

0.1nm Mg

Mg2p core level

Inte

nsity

/ cp

s*m

A-1

537 534 531 528 525bare PTCDA

3.2nm Mg

1.6nm Mg

0.4nm Mg

Inte

nsity

/ cp

s*m

A-1

Binding energy / eV

1 cp

s*m

A-1

0.1nm Mg

O1s core level

538 536 534 532 530 528

9nm Mg

3.3nm Mg

0.8nm Mg

Inte

nsity

/ cp

s*m

A-1

Binding energy / eV

bare DiMe-PTCDI

0.1nm Mg

O1s core level

1 cp

s*m

A-1

Mg onto Perylene Derivatives - O1s

MgO formationYes No

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

Simona Silaghi

Spectroscopic Ellipsometry(SE)

Reflectance AnisotropySpectroscopy (RAS)

variable angle of incidence

)iexp(tanrr

ρs

p ∆Ψ==

+ΦΦ+Φ=

ρ1ρ1ε 0

20

20

2 -tansinsin~

near normal incidencethe RAS signal:the effective dielectric function:

with: Φ0 - angle of incidence,rp, rs – Fresnel coefficients

and

βα

βα

rr

rr

+−

=∆

rr

2

where α and β correspond to[-110] and [110] directionsin the surface plane of a (001) oriented substrate

RAS

SE Φ0

Substrate

Polarisation DependentLinear Optical Techniques

Analysis of molecular-beam epitaxial growth of InAs on GaAs(100) by reflection anisotropy spectroscopy

S. M. Scholz, A. B. Müller, W. Richter, and D. R. T. ZahnDepartment of Physics, Technische Universität Berlin, Berlin, Germany

D. I. Westwood, D. A. Woolf, and R. H. WilliamsDepartment of Physics, University of Wales at Cardiff, United Kingdom

The molecular-beam epitaxial growth of InAs on GaAs(100) was investigated in situ using reflection anisotropy spectroscopy (RAS) and simultaneously

reflection high-energy electron diffraction. The RAS spectra of the GaAs c(4×4) and (2×4) and the InAs (4×2) and (2×4) reconstructions are reported. During

InAs deposition, the RAS signal shows significant changes for InAs coveragesas low as 1/6 of a monolayer. At this coverage surface reconstructions are

responsible for the signal variation. For InAs coverages larger than four monolayers, the RAS signal is essentially determined by the anisotropic

roughness of the three-dimensional growing surface. This is verified using a three-layer model which gives an excellent description of the experimental

spectra at large coverages.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures -- July 1992 -- Volume 10, Issue 4, pp. 1710-1715

2 3 4 50.0

0.4

0.8

1.2

S-GaAs(001):(2x1)

103 R

e(∆r

/r)

Energy / eV

E'0, E2E1, E1+∆1

RA Spectrum of S-GaAs(001):(2x1)

• Bulk-like features inducedby the reconstructedsurface

S–S[1]

Ga–S[2]

[1] G. Hughes et al., J. Appl. Phys. 78 (3), 1948 (1995)[2] V. L. Berkovits, D. Paget, Appl. Phys. Lett. 61 (15), 1835 (1992)

PTCDA10 nm

5 nm3 nm1 nm

GaAs

PTCDA features occur at ultra-low coverage!

extremely strong features around 4.5 –5.3 eV are interference and/or absorption related!GaAs

Evolution of RA Spectra uponPTCDA Deposition

BiomoleculesBiomolecules -- DNA DNA BasesBases

Thymine (T) Thymine (T) CC55HH66NN22OO22

Adenine (A)Adenine (A)CC55HH55NN55

Guanine (G)Guanine (G)CC55HH55NN55OO

Cytosine (C)Cytosine (C)CC44HH55NN33OO

Monatomic Regular Steps on Si(111)-3º

9.0nm5.7nm

0 5 10 15 2000.20.40.60.811.21.4

X[nm]

Z[nm]

5.7nm

Monatomic layer on each step (0.3 nm/layer)

Equidistant terraces

Atomically straight edges

Experimental slope ~ Nominal value of wafer

~2.8°

After 30sec. x 2times of flash

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

Yu Suzuki

Vicinal Silicon Surface

“(silicon) stepped surfaces can serve as templates for producing one-dimensional wires or stripes,”J. Viernow et al., Appl. Phys. Lett. 72, 948, 1998.

Steps and terraces are formed to compensate vicinal angle.

in in situsitu RAS RAS monitoringmonitoring ofof GuanineGuaninegrowngrown ontoonto vicinalvicinal H:Si(111)H:Si(111)--6°6°

1 2 3 4 5 6

0.0

0.5

1.0

1.5

2.0

E'0,E1

E2

103

Re(∆r

/r)

Energy / eV

10 nm 8 nm 6 nm 4 nm H:Si(111)-6°

With increasinglayer thickness:

•increase in themagnitude of theRAS signal,

• a slight shift of E2 towards lowerenergy.

Simulation of Simulation of ∆∆r/r r/r ––EffectEffect of of ThicknessThickness

1 2 3 4 5 6

0

2

4E2

E'0,E1

10 nm 8 nm 6 nm 4 nm 2 nm H:Si(111)-6°

103

Re(∆

r/r)

Energy / eV

aT. Yasuda, D. E. Aspnes, D. R. Lee, C. H. Bjiorkman, G. Lucovsky, J. Vac. Sci. Technol. A 12 (1994) 1152bT. U. Kampen, U. Rossow, M. Schumann, S. Park, D. R. T. Zahn, J. Vac. Sci. Technol. B 18 (2000) 2077

3-phase modela,b

(1)substrate: H:Si(111)-6°

(2) overlayer: Cauchy layer

(3) ambient,εa=1

measured∆r (d=0)r

simulation measured

o o∆r ∆r(d)~ (d=0)*f(ε ,n ,d)

r r

o oε ,n (λ),k = 0,d

o 2

Bn (λ) = A + ; A =1.45, B = 0.01.λ

in in situsitu RAS RAS monitoringmonitoring of of CytosineCytosinegrowngrown ontoonto vicinalvicinal H:Si(111)H:Si(111)--6°6°

1 2 3 4 5 6

0

2

4

6

8

10E2

E'0,E1

Energy / eV

103

Re(∆

r/r)

10 nm 8 nm 4 nm 2 nm H:Si(111)-6°

With increasing layerthickness:

•increase in themagnitude of the RASsignal,

• a slight shift of E2towards lower energy,

• larger anisotropysignal compared to guanine due to absorptionabsorptioncontribution.

absorptionband

1 2 3 4 5 6-100

-75

-50

-25

0

1 2 3 4 5 6

-2

0

2 103 R

e(∆r/r)

103

Re(∆r

/r)

Energy / eV

H:Si(111)-6° 2 nm 4 nm 7 nm 10 nm

E'0,E1

E2

H:Si(111)-6° 0.5 nm 1 nm 2 nm

in in situsitu RAS RAS monitoringmonitoring of of ThymineThyminegrowngrown ontoonto vicinalvicinal H:Si(111)H:Si(111)--6°6°

With increasinglayer thickness:

• extremely large anisotropies in theabsorption rangeof Thymine.

• surfaceroughnesscontribution.

in in situsitu RAS RAS monitoringmonitoring of of AdenineAdeninegrowngrown ontoonto vicinalvicinal H:Si(111)H:Si(111)--6°6°

1 2 3 4 5 6

-50

0

50

100

1 2 3 4 5 6

-5

0

5

103

Re(∆

r/r)

Energy / eV

H:Si(111)-6° 2 nm 4 nm 7 nm 8 nm 10 nm

E2E'0,E1

103 R

e(∆r/r)

H:Si(111)-6° 0.5 nm 1 nm 1.5 nm 2 nm

With increasinglayer thickness:

• large anisotropiesin the absorptionrange of Adenine,

• weaker RAS signal compared to Thymine.

1 2 3 4 5 6-50

-25

0

25

50

E2E'0,E1

Energy / eV

103

Re(∆r

/r)

H:Si(111)-3° 2 nm 4 nm 6 nm 8 nm 9.5 nm

in in situsitu RAS RAS monitoringmonitoring of of AdenineAdeninegrowngrown ontoonto vicinalvicinal H:Si(111)H:Si(111)--3°3°

• Lower offcutangle inducessmaller anisotropyby a factor of almost 2 comparedto H:Si(111)-6°.

1 2 3 4 5 6

-2

0

2

4

103

Re(∆

r/r)

Energy / eV

H:Si(111) 4 nm 6 nm 8 nm 10 nm

in in situsitu RAS RAS monitoringmonitoring of of AdenineAdeninegrowngrown ontoonto „„flatflat“ “ H:Si(111)H:Si(111)--0.35°0.35°

• Lower offcut angle induces smalleranisotropy by a factor of almost 40 compared to H:Si(111)-3°.

1 2 3 4 5 6-20

-10

0

10

20

30

103 R

e(∆r

/r)

Energy / eV

H:Si(111)-0.35°, (x10) H:Si(111)-3° H:Si(111)-6°

RAS RAS spectraspectra of 4 nmof 4 nm AdenineAdenine::EffectEffect of of VicinalityVicinality

the magnitude of the RAS signalscales linearly withthe offcut angle.

0 1 2 3 4 5 60

10

20

103 R

e(∆r

/r)

H:Si(111)-0.35° H:Si(111)-3° H:Si(111)-6°

Offcut Angle / °

Chemnitz Semiconductor Physicsand Organic Semiconductor Groups

Januar 2005

Ovidiu Gordan

BESSY VUV-XUV Ellipsometer Setup

• in situ vacuum ultraviolet spectroscopic ellipsometry (VUV-SE) in the range 4-10eV.• ex situ variable angle spectroscopic ellipsometry (VASE) in the range 0.8-5eV.

Ultra-Violet Ellipsometry of Ultra Thin Organic LayersUsing Synchrotron Radiation

O. D. Gordan et al., Appl. Phys. Letters submitted

Dielectric Function for Ultra-thin OrganicLayers Determined via VUV-Ellipsometry

Dr. Cameliu Himcinschi

Buried Interface Layer in Bonded Silicon Wafers

cross-section detail of active area (SEM picture)

Microscanner array bondedusing low temperature direct bonding

Si

Si

silicon oxide

Si

Si

silicon oxidesilicon oxideSi

Si

silicon oxide

EllipsometryEllipsometry

⇓Thickness

of surface oxide

Infrared SpectroscopyInfrared SpectroscopyTransmission Multiple Internal

Transmission (MIT)

Transmission Electron Transmission Electron Microscopy (TEM)Microscopy (TEM)

wafer bonds after etching

⇓Thickness of

interface oxide layer⇓

⇓

⇓Thermal relaxationof silicon oxide

Evolution of interfacial chemical species

Strategy for Wafer Bond Studies

1000 1500 2000 2500 3000 3500 40000.0

0.1

0.2

0.4

0.5

Si phononsabsorption

Tran

smitt

ance

Wavenumbers / cm-1

Single Transmission MIT

Interface Layer in Si-Si Bonded Wafersstudied by

Multiple Internal Transmission IR Spectroscopy

θint

MIT

Single Transmission

CHxOy-SiHx H-OH

Si-OH

Good agreement between IR and TEM dataAdvantagesAdvantages of IR:– Non-destructive technique– Determination of buried interface

thickness for the prebonded sample

Thickness of surface and interfaces oxides

400°C 800°C 1100°C

0 300 600 900 12003

4

5

6

10

11 SE - surface IR - interface HRTEM - interface

Thic

knes

s / n

m

Temperature / °C

In situ MIT Measurements during Annealing

3200 3400 3600 3800

RIE

RCA

O2 plasma

RT100°C125°C150°C175°C200°C225°C2*10-4M

IT T

rans

mitt

ance

per

pas

s

Wavenumber / cm-1

Rearrangement of HOHHOHand SiOHSiOH species at the interface with annealing depends on sample preparation.

Thanks to:

EU funded research Training Network DIODE (Contract No.: HPRN-CT-1999-00164)

OFET

DFG Schwerpunkt 1121

DS

G