a fourier transform infrared absorption study of hydrogen and deuterium in hydrothermal zno -master...
TRANSCRIPT
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_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
http://upload.wikimedia.org/wikipedia/en/8/8a/Electromagnetic-Spectrum.png
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
Molecular processes
http://upload.wikimedia.org/wikipedia/en/8/8a/Electromagnetic-Spectrum.png
e-
Bond breaking and ionization
Electronic excitation
Vibration
Rotation
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
1. Wavelength separation 2. Slit
3. Sample
4. Detectorv
5. Computer
I
FTIR
The Michelson interferometer principle 1. example: Monochromatic light
Detector
Movable mirror
Stationary Mirror
Beamsplitter
Interference
δ = Optical Path Difference
δ = (n + ½) λ
δ = n λ
FTIR
Dichromatic source
v
I
δ- l - /2l 0 /2 l l
I
Moveable mirror
FTIR
Broadband source
v
Continuous IR spectrum Interferogram
δ0
I I
Fourier Transform
Time domain: I vs. δ Frequency domain: I vs. v
FT
δ
I
v
I
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
Shi et. al. Physical Review B, 73(8):81201, 2006Li et. al. Physical Review B, 78(11), 2008.
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
Depth
Lo
g c
on
cen
tra
tion
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
O-face Zn-face
H-implantation: E = 1.1 MeV D-implantation: E = 1.4 MeV Dose: 2 x 1016 cm-2 on both sides
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
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
Quantification of the hydrogen content…
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