Wurtzite structure Sc1-xAlxN solid solution films grown by reactive magnetron sputter epitaxy: Structural characterization and first-principles calculations

AlN(0001) was alloyed with ScN with molar fractions up to similar to 22%, while retaining a single-crystal wurtzite (w-) structure and with lattice parameters matching calculated values. Material synthesis was realized by magnetron sputter epitaxy of thin films starting from optimal conditions for the formation of w-AlN onto lattice-matched w-AlN seed layers on Al2O3(0001) and MgO(111) substrates. Films with ScN contents between 23% and similar to 50% exhibit phase separation into nanocrystalline ScN and AlN, while ScN-rich growth conditions yield a transformation to rocksalt structure Sc1-xAlxN(111) films. The experimental results are analyzed with ion beam analysis, x-ray diffraction, and transmission electron microscopy, together with ab initio calculations of mixing enthalpies and lattice parameters of solid solutions in wurtzite, rocksalt, and layered hexagonal phases. (C) 2010 American Institute of Physics. [doi:10.1063/1.3448235]