A Fourier transform infrared absorption study of hydrogen and deuterium in hydrothermal ZnO

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A Fourier transforminfrared absorption study of
hydrogen and deuteriumin hydrothermal ZnO

• -Master presentation 14. Jan 2009
• -Hans Bjørge Normann
• -Web http//folk.uio.no/hansno/filer/MASTER_Fina
  l_15des.pdf

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Outline

• 1. Background
• Zinc Oxide
• Infrared Radiation
• Molecular processes
• FTIR / Spectrometry
• 2. Measurements
• 3. Hydrogen in ZnO
• 4. Isotopic substitution
• 5. Results
• 6. Conclusion

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FTIR - Introduction

• Study the interaction between infrared light and
  matter
• Non destructive
• Applications
• Identification of compounds in chemistry
• Study impurities in semiconductors

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Zinc Oxide

• Semiconductor with Eg3.4 eV
• Hexagonal wurtzite type structure
• Our sample dimensions 10x10x0.5 mm

5
Some ZnO applications

• Optical devices
• Transparent Conductive Oxide (TCO)
• Blue/UV Light Emitting Diodes (LEDs)
• Issues
• Ohmic and schottky contacts
• P-type doping
• Growth
• Impurities and crystal defects

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Infrared radiation

• Wavenumber

Region cm-1 µm eV
Near 12000 4000 0.8 2.5 1.55 0.5
Mid 4000 400 2.5 25 0.5 0.05
Far 400 10 25 1000 0.05 0.0012
http//upload.wikimedia.org/wikipedia/en/8/8a/Elec
tromagnetic-Spectrum.png
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Molecular processes
e-
Bond breaking and ionization
Electronic excitation
Vibration
Rotation
http//upload.wikimedia.org/wikipedia/en/8/8a/Elec
tromagnetic-Spectrum.png
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Infrared absorption

• IR absorption by defects
• Energy is transferred into quantized vibrational
  excitations

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2. Measurements

• 1. Background
• Zinc Oxide
• Infrared Radiation
• Molecular processes
• FTIR / Spectrometry
• 2. Measurements
• 3. Hydrogen in ZnO
• 4. Isotopic substitution
• 5. Results
• 6. Conclusion

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Absorption vs. wavenumber

• How can we obtain an intensity scan for many
  wavenumbers?
• 2 main methods
• Dispersion spectrometer
• FTIR

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Dispersion spectrometer
I
3. Sample
v
4. Detector
1. Wavelength separation
2. Slit
5. Computer
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FTIR

• The Michelson interferometer principle
• 1. example Monochromatic light

Movable mirror
d Optical Path Difference
Interference
d n ?
Detector
Beamsplitter
Stationary Mirror
d (n ½) ?
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FTIR

• Dichromatic source

I
I
v
d
- l -l/2 0 l/2 l
Moveable mirror
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FTIR

• Broadband source

I
I
v
d
0
Continuous IR spectrum
Interferogram
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Fourier Transform
Time domain I vs. d
Frequency domain I vs. v
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Advantages of FTIR

• Throughput Advantage
• Circular aperture, high signal intensity ? high
  signal to noise ratio
• Multiplex Advantage
• All frequencies are measured at the same time
• Precision Advantage
• Internal laser control the scanner built in
  calibration

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FTIR _at_ MiNaLab

• Bruker IFS 113v (Genzel type interferometer)
• Detection limit 1014 - 1015 cm-3

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FTIR _at_ MiNaLab
Optical layout Sample holder
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Measurement

• Background spectrum I0
• Sample spectrum I

I0 I
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Fourier Transformed I vs v
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Absorbance

• Reflectivity
• Absorbance and Beer-Lambert Law
• d sample thickness
• c absorbant concentration
• a absorption coefficient

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3. Hydrogen in ZnO

• 1. Background
• Zinc Oxide
• Infrared Radiation
• Molecular processes
• FTIR / Spectrometry
• 2. Measurements
• 3. Hydrogen in ZnO
• 4. Isotopic substitution
• 5. Results
• 6. Conclusion

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Hydrogen in ZnO

• O-H configurations?
• LiO-H configurations?
• O-H stretch modes occurs "always" in the 3200 -
  3600 cm-1 region

Li et. al. Physical Review B, 78(11), 2008.
Shi et. al. Physical Review B, 73(8)81201, 2006
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4 samples

• V85 and V104
• Untreated (as-grown) samples
• Heat treated at 400 oC for 70 hours
• V91
• Ion implanted with hydrogen
• Heat treated at 400 oC for 70 hours
• V92
• Ion implanted with deuterium
• Heat treated at 400 oC for 70 hours

Log concentration
Depth
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4. Isotopic substitution

• 1. Background
• Zinc Oxide
• Infrared Radiation
• Molecular processes
• FTIR / Spectrometry
• 2. Measurements
• 3. Hydrogen in ZnO
• 4. Isotopic substitution
• 5. Results
• 6. Conclusion

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Isotopic substitution H and D

• Harmonic oscillator approximation
• Ratio between O-H and O-D frequency
• ? angular frequency, k force constant, µ
  reduced mass and M,m mass
• O-D modes expected at 2300 - 2600 cm-1

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5. Results

• 1. Background
• Zinc Oxide
• Infrared Radiation
• Molecular processes
• FTIR / Spectrometry
• 2. Measurements
• 3. Hydrogen in ZnO
• 4. Isotopic substitution
• 5. Results
• 6. Conclusion

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DTGS-detector measurements

• IR parallel to c-axis of the crystal
• As-grown samples

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Ion-implantation / SIMS

• H-implantation E 1.1 MeV
• D-implantation E 1.4 MeV
• Dose 2 x 1016 cm-2 on both sides

O-face Zn-face
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InSb-detector measurements

• IR parallel to c-axis
• As-grown samples
• Annealed

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InSb-detector measurements

• IR parallel to c-axis
• Hydrogen implanted
• Annealed
• Polished

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InSb-detector measurements

• IR parallel to c-axis
• Deuterium implanted
• Annealed
• Polished

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InSb-detector measurements

• IR perpendicular to c-axis

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InSb-detector measurements

• k perpendicular to c-axis measurements
• As-grown and annealed

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InSb-detector measurements

• k perpendicular to c-axis measurements
• Hydrogen implanted and annealed / polished

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InSb-detector measurements

• k perpendicular to c-axis measurements
• Deuterium implanted and annealed / polished

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Isotopic shifts
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Isotopic shifts
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Quanti?cation of the hydrogen content...

• Integrated absorbance (IA)
• Absorption strength per species
• D-dose (1.46 0.54) x 1017 cm-2
• IA (2644 peak) 0.233 cm -2
• ?D (1.72 0.63) x 10-18 cm

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Quanti?cation of the hydrogen content...

• Similar treatment on hydrogen is not easy
• A conversion factor is needed ?D x C ?H
• From other oxides C 1.31 (LiNbO3), 1.88 (TiO2)
• Approximation CZnO 1.595
• ?H (2.74 1.01) x 10-18 cm

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Quanti?cation of the hydrogen content

• Integrated absorbace of the 3577 cm-1 peaks
• ?H (2.74 1.01) x 10-18 cm
• Total H dose introduced 4 x 1016 cm-2
• Total H dose already present (V85) (2.8 1.0)
  x 1016 cm-2

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Possible defect identification

• 2644 / 3577 cm-1 peaks are assigned a OD-Li
  /OH-Li complex
• The rest of the peaks?
• O-H configurations that may be related to
  vacancies

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Suggestions for future work

• Implantation of higher H-dose
• Annealing time
• Polarizing filter
• Uni-axial stress

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6. Conclusion

• Eight vibrational modes excellent isotopic
  shifts!
• In addition, modes at 2613, 3279 and 3483 cm-1
• We observe previously unreported O-D modes
  close associated with defects involving vacancies
• Absorption strength per deuterium species has
  been determined
• Absorption strength per hydrogen species has been
  approximated
• O-H---Li configuration supported by SIMS/FTIR
• Introduced amount of H in the same order of
  magnitude compared to the dose already present

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Thank You

• Prof. Bengt Svensson, Dr. Leonid Murin, Viktor
  Bobal, Dr. Lasse Vines, Klaus Magnus Johansen,
  Dr. Jan Bleka, Hallvard Angelskår, Tariq Maqsood,
  Lars Løvlie, Anders Werner Bredvei Skilbred aka
  Fru Larsen and Øyvind Hanisch
• References
• Griffiths and Haseth, Fourier Transform Infrared
  Spectrometry
• Kittel, Introduction to Solid State Physics
• Ellmer, Klein, Rech, Transparent Conductive Zinc
  Oxide
• Bruker Optics
• Web
• http//folk.uio.no/hansno/filer/MasterPres.pdf
• http//folk.uio.no/hansno/filer/MasterPres.pptx
• http//folk.uio.no/hansno/filer/MASTER_Final_15des
  .pdf