| 1. |
- Ben Sedrine, Nabiha, et al.
(författare)
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Infrared dielectric functions and optical phonons of wurtzite YxAl1-xN (0 less than= x less than= 0.22)
- 2015
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 48:41, s. 415102-
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Tidskriftsartikel (refereegranskat)abstract
- YAlN is a new member of the group-III nitride family with potential for applications in next generation piezoelectric and light emitting devices. We report the infrared dielectric functions and optical phonons of wurtzite (0001) YxAl1-xN epitaxial films with 0 less than= x less than= 0.22. The films are grown by magnetron sputtering epitaxy on c-plane Al2O3 and their phonon properties are investigated using infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The infrared-active E-1(TO) and LO, and the Raman active E-2 phonons are found to exhibit one-mode behavior, which is discussed in the framework of the MREI model. The compositional dependencies of the E-1(TO), E-2 and LO phonon frequencies, the high-frequency limit of the dielectric constant, epsilon(infinity), the static dielectric constant, epsilon(0), and the Born effective charge Z(B) are established and discussed.
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| 2. |
- Tholander, Christopher, et al.
(författare)
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Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy
- 2016
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 105, s. 199-206
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Tidskriftsartikel (refereegranskat)abstract
- By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (YxIn1-xN). Ab initio calculations show that the YxIn1-xN wurtzite phase is lowest in energy among relevant alloy structures for 0≤x≤0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x=0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AlN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown YxIn1-xN films. The piezoelectric response in films with x=0.09 and x=0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict YxIn1−xN to have comparable piezoelectric properties to ScxAl1-xN.
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| 3. |
- Zukauskaite, Agne, et al.
(författare)
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Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
- 2015
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Ingår i: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 212:3, s. 666-673
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Žukauskaitė, Agnė, et al.
(författare)
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Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
- 2015
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 94, s. 101-110
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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