Microstructure of epitaxial Mg₃N₂ thin films grown by MBE

The epitaxial growth of Mg₃N₂ thin films by molecular beam epitaxy has been recently achieved. This work presents the structural properties of the films, including grain sizes and lattice rotations, as assessed by x-ray diffraction and transmission electron microscopy. The films’ microstructure consists of well-aligned columnar grains 10 nm in diameter that nucleate at the film/substrate interface and display a significant column twist, in the order of 2.5°. As growth proceeds, tilted and twisted mosaic blocks overgrow these columns, as observed in many other epitaxial semiconductors. Yet, the rocking curves on symmetric reflections display extremely narrow peaks (∼50 arc sec), revealing a long-range spatial correlation between structural defects that should not be mistakenly considered a proof of high crystalline quality.