ScN/GaN(11̅00): a new platform for the epitaxy of twin-free metal-semiconductor heterostructures

We study the molecular beam epitaxy of rock-salt ScN on the wurtzite GaN(11̅00) surface. To this end, ScN is grown on free-standing GaN(11̅00) substrates and self-assembled GaN nanowires that exhibit (11̅00) sidewalls. On both substrates, ScN crystallizes twin-free thanks to a specific epitaxial relationship, namely ScN(110)[001]||GaN(11̅00)[0001], providing a congruent, low-symmetry GaN/ScN interface. The 13.1 orientation mostly relaxes within the first few monolayers of growth by forming a coincidence site lattice, where 7 GaN planes coincide with 8 ScN planes, leaving the ScN surface nearly free of extended defects. Overgrowth of the ScN with GaN leads to a kinetic stabilization of the zinc blende phase, that rapidly develops wurtzite inclusions nucleating on 111 nanofacets, commonly observed during zinc blende GaN growth. Our ScN/GaN(11̅00) platform opens a new route for the epitaxy of twin-free metal-semiconductor heterostructures made of closely lattice-matched GaN, ScN, HfN and ZrN compounds.