Sputtered ferroelectric aluminum scandium boron nitride (Al1−x−yBxScyN)/ <i>n</i> -GaN heterostructures

Abstract

This work demonstrates ferroelectric switching in magnetron sputtered Al1−x−yBxScyN/n-GaN heterostructures. Using high power impulse magnetron sputtering, a silicon doped n-GaN bottom electrode with an electron concentration of 6.0 × 1019 cm−3 is grown on c-plane sapphire. Al1−x−yBxScyN films are prepared on the GaN surface with Al:B:Sc ratios that produce tensile, lattice matched, or compressive epitaxial strains. X-ray diffraction shows that lattice matched and compressively strained Al1−x−yBxScyN compositions are pseudomorphic, while partial relaxation is observed for tensilely strained Al1−x−yBxScyN/n-GaN heterostructures. Electrically, the Al1−x−yBxScyN/n-GaN stacks show robust hysteresis; the P–E loops are fully saturated with both lattice matched and compressively strained Al1−x−yBxScyN compositions exhibiting remanent polarization values of 135 μC/cm2. For comparison, Al1−x−yBxScyN films are also prepared on metal organic chemical vapor deposition and single crystal GaN substrates to extend strain and morphology trends to more common substrate types. This report validates that sputter deposition is a feasible technique for fabricating strain-tunable ferroelectric III–N heterostructures with high crystalline fidelity and smooth surface morphologies.