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.

AlN(0001) was alloyed with ScN with molar fractions up to $\sim 22\mathrm{\%}$ , while retaining a single-crystal wurtzite (w-) structure and with lattice parameters matching calculated values. Material synthesis was realized by magnetron sputter epitaxy of thin films starting from optimal conditions for the formation of w-AlN onto lattice-matched w-AlN seed layers on ${\text{Al}}_2{\text{O}}_3\left(0001\right)$ and MgO(111) substrates. Films with ScN contents between 23% and $\sim 50\mathrm{\%}$ exhibit phase separation into nanocrystalline ScN and AlN, while ScN-rich growth conditions yield a transformation to rocksalt structure ${\text{Sc}}_{1-\text{x}}{\text{Al}}_{\text{x}}\text{N}\left(111\right)$ films. The experimental results are analyzed with ion beam analysis, x-ray diffraction, and transmission electron microscopy, together with ab initio calculations of mixing enthalpies and lattice parameters of solid solutions in wurtzite, rocksalt, and layered hexagonal phases.

Alloys of scandium with AlN exhibit an enhanced piezoelectric coefficient that can boost the performance of nitride‐based electronic and optoelectronic devices such as high electron mobility transistors (HEMTs). Consequently, there is increasing interest in the epitaxial growth of high‐quality AlScN/GaN heterostructures. So far, only very recent reports on AlScN HEMT structures grown by molecular beam epitaxy (MBE) have been published. Herein, the motivation for depositing AlScN epitaxial layers by metal‐organic chemical vapor deposition (MOCVD) as well as the challenges associated with this approach are explained. For the first time, the successful deposition of epitaxial layers with a Sc content up to 30% (Al_0.7Sc_0.3N) is reported. It is shown that the deposited films consist of wurtzite‐type AlScN with high crystalline quality, demonstrating that MOCVD is suitable for the growth of HEMT structures with Sc‐based ternary nitrides.

Thermoelectric properties of ScN thin films grown by reactive magnetron sputtering on Al₂O₃(0001) wafers are reported. X-ray diffraction and elastic recoil detection analyses show that the composition of the films is close to stoichiometry with trace amounts (∼1 at. % in total) of C, O, and F. We found that the ScN thin-film exhibits a rather low electrical resistivity of ∼2.94 μΩm, while its Seebeck coefficient is approximately ∼−86 μV/K at 800 K, yielding a power factor of ∼2.5 × 10⁻³ W/mK². This value is anomalously high for common transition-metal nitrides.

Aluminum scandium nitride (Al_1−xSc_xN with x = 0–0.41) thin films were deposited by reactive pulsed-DC magnetron sputtering on Si(001) and Al₂O₃(0001) substrates. X-ray diffraction indicated high degree of c-axis orientation in all the films, and based on pole figure measurements, epitaxial relationship could be defined as $\left[10\overline{1}0\right]$ _AlScN//$\left[11\overline{2}0\right]$ _sapphire and (0001)_AlScN//(0001)_sapphire in films deposited on Al₂O₃. Piezoelectric coefficient increased up to d₃₃ = 31.6 pC/N in Al_0.59Sc_0.41N, which is 550% higher than for AlN. The biaxial elastic modulus and the in-plane coefficient of thermal expansion (CTE) as a function of Sc concentration were determined by thermal cycling method: biaxial elastic modulus decreased from 535 GPa in pure AlN to 269 GPa in Al_0.59Sc_0.41N and CTE was 4.65 × 10⁻⁶ K⁻¹ for AlN and 4.29 × 10⁻⁶ K⁻¹ for Al_0.59Sc_0.41N. Additionally, we observed an increase in CTE from 4.18 × 10⁻⁶ K⁻¹ at 65 °C to up to 6.38 × 10⁻⁶ K⁻¹ at 375 °C for Al_0.68Sc_0.32N. The experimentally determined CTE and elastic modulus allow a more precise design of Al_1−xSc_xN-based frequency filters which are used in mobile communications and are important parameters for the prediction of device performance at elevated temperatures.

Piezoelectric wurtzite Sc_xAl_1−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 Sc_xAl_1−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.