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

TL;DR

This study demonstrates the combinatorial synthesis of Al1-xRExN thin films with RE = Pr, Tb, revealing phase stability limits, structural transitions, and optoelectronic properties, advancing the understanding of rare earth doping in AlN materials.

Contribution

First comprehensive survey of RE incorporation into AlN thin films using combinatorial co-sputtering, revealing phase stability and optoelectronic effects at higher RE levels.

Findings

Pr and Tb can be incorporated into AlN up to higher levels than previously reported.

Phase transitions from wurtzite to amorphous occur at specific RE concentrations.

Optical absorption and cathodoluminescence properties depend on RE content and phases.

Abstract

The potential impact of cation-substituted AlN-based materials, such as Al1-xScxN, Al1-xGaxN, and Al1-xBxN, 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 Al1-xRExN (RE = Pr, Tb) thin films and performed a rapid survey of the composition-structure-property relationships as a function of RE alloying. Under our growth conditions, we observe that Al1-xPrxN maintains a phase-pure wurtzite structure until transitioning to amorphous for x>0.22. Al1-xTbxN 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.