ScN/GaN($1\bar{1}00$): 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($1\bar{1}00$) surface. To this end, ScN is grown on free-standing GaN($1\bar{1}00$) substrates and self-assembled GaN nanowires that exhibit ($1\bar{1}00$) sidewalls. On both substrates, ScN crystallizes twin-free thanks to a specific epitaxial relationship, namely ScN(110)[001]$||$GaN($1\bar{1}00$)[0001], providing a congruent, low-symmetry GaN/ScN interface. The 13.1 % uniaxial lattice mismatch occurring in this 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($1\bar{1}00$) 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.