Combinatorial synthesis and characterization of thin film Al1−xRExN (RE = Pr3+ and Tb3+) heterostructural alloys

Abstract

The potential impact of cation-substituted AlN-based materials, such as Al_1−xSc_xN, Al_1−xGa_xN, and Al_1−xB_xN, with exceptional electronic, electromechanical, and dielectric properties has spurred research into this broad family of materials. Rare earth (RE) cations are particularly appealing as they could additionally impart optoelectronic or magnetic functionality. However, success in incorporating a significant level of RE cations into AlN has been limited so far because it is thermodynamically challenging to stabilize such heterostructural alloys. Using combinatorial co-sputtering, we synthesized Al_1−xRE_xN (RE = Pr, Tb) thin films and performed a rapid survey of the composition–structure–property relationships as a function of RE substitution. Under our growth conditions, we observe that Al_1−xPr_xN maintains a phase-pure wurtzite structure until transitioning to amorphous for x ≳ 0.22. Al_1−xTb_xN exhibits a phase-pure wurtzite structure until x ≲ 0.15, then exhibits mixed wurtzite and rocksalt phases for 0.16 ≲ x ≲ 0.28, and finally becomes amorphous beyond that. Ellipsometry measurements reveal that the absorption onset decreases with increasing rare earth incorporation and has a strong dependence on the phases present. We observe the characteristic cathodoluminescence emission of Pr³⁺ and Tb³⁺, respectively. Using this synthesis approach, we have demonstrated incorporation of Pr and Tb into the AlN wurtzite structure up to higher compositions levels than previously reported and made the first measurements of corresponding structural and optoelectronic properties.