A FOURIER TRANSFORM INFRARED ABSORPTION STUDY OF HYDROGEN AND DEUTERIUM IN HYDROTHERMAL ZNO -Master presentation 14. Jan Hans Bjørge Normann -Web:

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 E g =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

Molecular processes e-e- e-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. Detector v 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 -  -  0  I Moveable mirror

FTIR  Broadband source v Continuous IR spectrumInterferogram δ 0 II

Fourier Transform Time domain: I vs. δFrequency 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

MiNaLab  Bruker IFS 113v (Genzel type interferometer)  Detection limit ~ cm -3

MiNaLab Optical layoutSample holder

Measurement  Background spectrum = I 0  Sample spectrum = I I 0 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, 2006 Li et. al. Physical Review B, 78(11), 2008.

4 samples  V85 and V104  Untreated (as-grown) samples  Heat treated at 400 o C for 70 hours  V91  Ion implanted with hydrogen  Heat treated at 400 o C for 70 hours  V92  Ion implanted with deuterium  Heat treated at 400 o C for 70 hours Depth Log concentration

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-faceZn-face  H-implantation: E = 1.1 MeV  D-implantation: E = 1.4 MeV  Dose: 2 x 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

Quantification of the hydrogen content...  Integrated absorbance (IA)  Absorption strength per species  D-dose: (1.46 ± 0.54) x cm -2  IA (2644 peak): cm -2   D = (1.72 ± 0.63) x 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 (LiNbO 3 ), 1.88 (TiO 2 )  Approximation C ZnO ~   H = (2.74 ± 1.01) x cm

 Integrated absorbace of the 3577 cm -1 peaks   H = (2.74 ± 1.01) x cm  Total H dose introduced: 4 x cm -2  Total H dose already present (V85): (2.8 ± 1.0) x 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   