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Metastable ScAlN and YAlN Thin Films Grown by Reactive Magnetron Sputter Epitaxy
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metastable ScxAl1-xN and YxAl1-xN thin films were deposited in an ultra high vacuum system using reactive magnetron sputter epitaxy from elemental Al, Sc, and Y targets in Ar/N2 gas mixture. Their structural, electrical, optical, mechanical, and piezoelectrical properties were investigated by using the transmission electron microscopy, x-ray diffraction, spectroscopic ellipsometry, I-V and C-V measurements, nanoindentation, and two different techniques for piezoelectric characterization: piezoresponse force microscopy and double beam interferometry.

Compared to AlN, improved electromechanical coupling and increase in piezoelectric response was found in ScxAl1-xN/TiN/Al2O3 structures with Sc content up to x=0.2. Decreasing the growth temperature down to 400 °C improved the microstructure and crystalline quality of the material. Microstructure of the films had a stronger influence on piezoelectric properties than the crystalline quality, which affected the leakage currents. When x was increased from x=0 to x=0.3, the hardness and reduced Young’s modulus Er showed a decrease from 17 GPa to 11 GPa, and 265 GPa down to 224 GPa, respectively. In ScxAl1-xN/InyAl1-yN superlattices, ScxAl1-xN layers negative lattice mismatched to In-rich InyAl1-yN were found to be stable at higher Sc concentration (x=0.4) than lattice-matched or positive lattice mismatched layers, confirmed by first principle (ab initio) calculations using density-functional formalism.

Al-rich YxAl1-xN thin films were synthesized and reported for the first time. Formation of solid solution was observed up to x=0.22 and an increase in growth temperature up to 900°C improved the crystalline quality of the YxAl1-xN films. The band gap of YxAl1-xN decreased from 6.2 eV for AlN down to 4.5 eV (x=0.22) and was shown to follow Vegard’s rule. Refractive indices and extinction coefficients were also determined. Lattice constants of wurtzite YxAl1-xN measured experimentally are in good agreement with theoretical predictions obtained through ab initio calculations. The mixing enthalpy

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 64 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1564
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-103832DOI: 10.3384/diss.diva-103832ISBN: 978-91-7519-434-9 (print)OAI: oai:DiVA.org:liu-103832DiVA: diva2:691894
Public defence
2014-02-21, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Increased electromechanical coupling in w-ScxAl1-xN
Open this publication in new window or tab >>Increased electromechanical coupling in w-ScxAl1-xN
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2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, no 11, 112902- p.Article in journal (Refereed) Published
Abstract [en]

AlN is challenged as the material choice in important thin film electroacoustic devices for modern wireless communication applications. We present the promise of superior electromechanical coupling (kt2), in w−ScxAl1−xN by studying its dielectric properties. w−ScxAl1−xN (0≤x≤0.3) thin films grown by dual reactive magnetron sputtering exhibited low dielectric losses along with minor increased dielectric constant (ε). Ellipsometry measurements of the high frequency ε showed good agreement with density function perturbation calculations. Our data show that kt2 will improve from 7% to 10% by alloying AlN with up to 20 mol % ScN.

 

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-59839 (URN)10.1063/1.3489939 (DOI)000282032900055 ()
Note
Original Publication: Gunilla Wingqvist, Ferenc Tasnadi, Agne Zukauskaite, Jens Birch, Hans Arwin and Lars Hultman, Increased electromechanical coupling in w-ScxAl1-xN, 2010, Applied Physics Letters, (97), 11, 112902. http://dx.doi.org/10.1063/1.3489939 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-09-27 Created: 2010-09-27 Last updated: 2017-12-12Bibliographically approved
2. Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
Open this publication in new window or tab >>Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 9, 093527- p.Article in journal (Refereed) Published
Abstract [en]

Piezoelectric wurtzite ScxAl1-xN (x=0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. Samples grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN samples grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x≥0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1-xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x=0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76471 (URN)10.1063/1.4714220 (DOI)000304109900044 ()
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved
3. Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
Open this publication in new window or tab >>Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
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2015 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 3, 666-673 p.Article in journal (Refereed) Published
Abstract [en]

Nanoindentation with in-situ electrical characterization was used to characterize piezoelectric scandium aluminum nitride (ScxAl1-xN) thin films with Sc contents up to x=0.3. The films were prepared by reactive magnetron sputtering using Al2O3 substrates with TiN seed layer/bottom electrodes at a substrate temperature of 400 °C. X-ray diffraction shows c-axis oriented wurtzite ScxAl1-xN, where the crystal quality decreases with increasing x. Piezoresponse force microscopy in mapping mode shows a single piezoelectric polarization phase in all samples. The hardness and decreases from 17 GPa in AlN to 11 GPa in Sc0.3Al0.7N, while reduced elastic modulus decreases from 265 GPa to 224 GPa, respectively. Both direct and converse piezoelectric measurements are demonstrated by first applying the load and generating the voltage and later by applying the voltage and measuring film displacement using a conductive boron doped nanoindenter tip. The Sc0.2Al0.8N films exhibit an increase in generated voltage by 15% in comparison to AlN and a correspondingly larger displacement upon applied voltage, comparable to results obtained by double beam interferometry and piezoresponse force microscopy.

 

Place, publisher, year, edition, pages
John Wiley & Sons, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-103830 (URN)10.1002/pssa.201431634 (DOI)000351530800029 ()
Note

On the day of the defence date of the Ph.D. Thesis, the status of this article was Manuscript.

Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
4. Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
Open this publication in new window or tab >>Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
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2015 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 94, 101-110 p.Article in journal (Refereed) Published
Abstract [en]

Pseudomorphic stabilization in wurtzite ScxAl1-xN/AlN and ScxAl1-xN/InyAl1-yN superlattices (x=0.2, 0.3, and 0.4; y=0.2-0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1-xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1-xN/InyAl1-yN superlattices a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1-xN even for the highest investigated concentration x=0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1-xN under tensile stress when x≥0.375 and support the experimental results.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-103831 (URN)10.1016/j.actamat.2015.04.033 (DOI)000357143500010 ()
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
5. YxAl1-xN Thin Films
Open this publication in new window or tab >>YxAl1-xN Thin Films
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2012 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 42, 422001- p.Article in journal (Refereed) Published
Abstract [en]

Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76472 (URN)10.1088/0022-3727/45/42/422001 (DOI)000309766700001 ()
Note

funding agencies|Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Research Council (VR)|349-2008-6582|FCT Portugal|SFRH/BPD/66818/2009|VR|2010-3848|Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved
6. Bandgap Engineering and Optical Constants of YxAl1-xN Alloys
Open this publication in new window or tab >>Bandgap Engineering and Optical Constants of YxAl1-xN Alloys
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2013 (English)In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 52, no 8Article in journal (Refereed) Published
Abstract [en]

We study wurtzite Yx Al1-xN (0 andlt;= x andlt;= 0:22) films with (0001) orientation deposited by magnetron sputtering epitaxy on Si(100) substrates and we determine the alloys band gap energies and optical constants. Room temperature spectroscopic ellipsometry (SE) is employed in the energy range from 1 to 6.3 eV, and data modeling based on the standard dielectric function model is used. As a result of the SE data analysis the Yx Al1-xN refractive index and extinction coefficient are determined. The band gap of Yx Al1-xN is found to decrease linearly from 6.2 eV (x=0) down to 4.5 eV (x=0:22). We further observe an increase of the refractive index with increasing Y content; from 1.93 to 2.20 (at 2 eV) for x=0 and 0.22, respectively, reflecting the increase in material density.

Place, publisher, year, edition, pages
Japan Society of Applied Physics, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-98153 (URN)10.7567/JJAP.52.08JM02 (DOI)000323883100159 ()
Note

Funding Agencies|FCT|REF:SFRH/BPD/66818/2009|Swedish Research Council (VR)|2010-3848|Linko "ping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06

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