Structural optimization of lattice-matched Sc0.14Al0.86N/GaN superlattices for photonic applications

TL;DR

This study systematically investigates the molecular-beam epitaxy of lattice-matched Sc0.14Al0.86N/GaN superlattices, revealing optimal growth conditions and the importance of temperature-dependent intermixing for photonic device applications.

Contribution

It provides a detailed analysis of lattice-matching conditions, interfacial intermixing, and optimal growth parameters for ScAlN/GaN superlattices, advancing their integration in quantum photonics.

Findings

Lattice-matching achieved at x=0.14 Sc composition.

Strain-induced defects occur when deviating from lattice-matching.

Optimal growth temperatures identified at ~600°C and ~550°C.

Abstract

ScxAl1-xN is an emerging III-nitride material known for its high piezoelectric coefficient and ferroelectric properties. Integration of wide-bandgap ScxAl1-xN with GaN is particularly attractive for quantum photonic devices. Achieving low defect complex multilayers incorporating ScxAl1-xN, though, requires precise lattice-matching and carefully optimized growth parameters. This study systematically investigates the molecular-beam epitaxy of short-period ScxAl1-xN/GaN superlattices with total thicknesses of up to 600 nm on GaN templates. X-ray diffraction reciprocal space mapping confirmed lattice-matching at x = 0.14 Sc composition regardless of the thickness of GaN interlayers, as evidenced by symmetric superlattice satellites aligned in-plane with the underlying substrate peak. Superlattices with Sc compositions deviating from this lattice-matching condition exhibited strain-induced defects ranging from crack formation to partial relaxation. Scanning transmission electron microscopy (STEM) investigation of the ScxAl1-xN/GaN interfaces identified temperature-dependent intermixing as a major factor in setting the nitride composition variation and implicitly band structure profile along the growth direction. Energy-dispersive X-ray spectroscopy also revealed that Sc incorporation exhibits delays relative to Al at both onset and termination. Optimal growth conditions were observed at approximately 600{\deg}C and 550{\deg}C for superlattices with thick GaN layers (6 nm), and ultra-thin GaN layers (< 2 nm), respectively.