A FOURIER TRANSFORM
INFRARED ABSORPTION
STUDY OF
HYDROGEN AND DEUTERIUM
IN HYDROTHERMAL ZNO
-Master presentation 14. Jan 2009
-Hans Bjørge Normann
-Web: http://folk.uio.no/hansno/filer/MASTER_Final_15des.pdf
Outline

1. Background
Zinc Oxide
 Infrared Radiation
 Molecular processes
 FTIR / Spectrometry






2. Measurements
3. Hydrogen in ZnO
4. Isotopic substitution
5. Results
6. Conclusion
FTIR - Introduction



Study the interaction between infrared light and
matter
Non destructive
Applications:
 Identification of compounds in chemistry
 Study impurities in semiconductors
Zinc Oxide



Semiconductor with Eg=3.4 eV
Hexagonal wurtzite type structure
Our sample dimensions = 10x10x0.5 mm
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
Infrared radiation

Wavenumber
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
Region
http://upload.wikimedia.org/wikipedia/en/8/8a/Electromagnetic-Spectrum.png
Molecular processes
e-
Bond breaking and ionization
Electronic excitation
Vibration
Rotation
http://upload.wikimedia.org/wikipedia/en/8/8a/Electromagnetic-Spectrum.png
Infrared absorption


IR absorption by defects
Energy is transferred into quantized vibrational excitations
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
Absorption vs. wavenumber


How can we obtain an intensity scan for many wavenumbers?
2 main methods


Dispersion spectrometer
FTIR
Dispersion spectrometer
I
3. Sample
1. Wavelength separation
v
4. Detector
2. Slit
5. Computer
FTIR


The Michelson interferometer principle
1. example: Monochromatic light
Movable mirror
δ = Optical Path Difference
Interference
δ=nλ
Detector
Stationary
Mirror
Beamsplitter
δ = (n + ½) λ
FTIR

Dichromatic source
I
I
v
δ
- l -l/2 0 l/2 l
Moveable mirror
FTIR

Broadband source
I
I
v
0
Continuous IR spectrum
Interferogram
δ
Fourier Transform
FT
I
I
δ
Time domain: I vs. δ
v
Frequency domain: I vs. v
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
FTIR @ MiNaLab

Bruker IFS 113v (Genzel type interferometer)

Detection limit ~1014 - 1015 cm-3
FTIR @ MiNaLab
Optical layout
Sample holder
Measurement

Background spectrum = I0

Sample spectrum = I
I0
I
Fourier Transformed – I vs v
Absorbance

Reflectivity

Absorbance and Beer-Lambert Law



d = sample thickness
c = absorbant concentration
α = absorption coefficient
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
Hydrogen in ZnO

O-H configurations?

Li···O-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
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
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
Isotopic substitution – H and D


Harmonic oscillator approximation

Ratio between O-H and O-D frequency

ω = angular frequency, k = force constant, µ = reduced mass and M,m = mass
O-D modes expected at 2300 − 2600 cm−1
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
DTGS-detector measurements

IR parallel to c-axis of the crystal
 As-grown
samples
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
InSb-detector measurements

IR parallel to c-axis


As-grown samples
Annealed
InSb-detector measurements

IR parallel to c-axis



Hydrogen implanted
Annealed
Polished
InSb-detector measurements

IR parallel to c-axis



Deuterium implanted
Annealed
Polished
InSb-detector measurements

IR perpendicular to c-axis
InSb-detector measurements

k perpendicular to c-axis measurements

As-grown and annealed
InSb-detector measurements

k perpendicular to c-axis measurements

Hydrogen implanted and annealed / polished
InSb-detector measurements

k perpendicular to c-axis measurements

Deuterium implanted and annealed / polished
Isotopic shifts
Isotopic shifts
Quantification 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
Quantification 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
Quantification 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
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
Suggestions for future work




Implantation of higher H-dose
Annealing time
Polarizing filter
Uni-axial stress
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
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