a fourier transform infrared absorption study of hydrogen and deuterium in hydrothermal zno -master...

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