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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
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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_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
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 v 4. Detector 1. Wavelength separation 2. Slit 5. Computer
FTIR • The Michelson interferometer principle • 1. example: Monochromatic light Movable mirror δ= Optical Path Difference Interference δ= n λ Detector Beamsplitter StationaryMirror 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 δ 0 Continuous IR spectrum Interferogram
Fourier Transform δ FT I I v Time domain: I vs. δ 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
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 • IRparallel 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-axismeasurements • As-grown and annealed
InSb-detector measurements • k perpendicular to c-axismeasurements • Hydrogen implanted and annealed / polished
InSb-detector measurements • k perpendicular to c-axismeasurements • Deuterium implanted and annealed / polished
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: Dx 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