Cubic Sc1−xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111)

Abstract

Reactive magnetron sputter epitaxy was used to deposit thin solid films of Sc1−xAlxN (0≤x≤1) onto MgO(111) substrates with ScN(111) seed layers. Stoichiometric films were deposited from elemental Sc and Al targets at substrate temperatures of 600 °C. The films were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection analysis, x-ray diffraction, and transmission electron microscopy. Results show that rocksalt structure (c)-Sc1−xAlxN solid solutions with AlN molar fractions up to ∼60% can be synthesized. For higher AlN contents, the system phase separates into c- and wurtzite structure (w)-Sc1−xAlxN domains. The w-domains are present in three different orientations relative to the seed layer, namely, Sc1−xAlxN(0001)∥ScN(111) with Sc1−xAlxN[1¯21¯0]∥ScN[11¯0], Sc1−xAlxN(101¯1)∥ScN(111) with Sc1−xAlxN[1¯21¯0]∥ScN[11¯0], and Sc1−xAlxN(101¯1)‖ScN(113). The results are compared to first-principles density functional theory calculations for the mixing enthalpies of c-, w-, and zinc blende Sc0.50Al0.50N solid solutions, yielding metastability with respect to phase separation for all temperatures below the melting points of AlN and ScN.