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.

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

“…11 In Ref. 20, the zinc-blende B3, structure was found to be considerably higher in energy as compared to cubic and wurtzite phases for Sc 0.5 Al 0.5 N and is thus excluded from this analysis. The cubic solid solution has been considered over the whole concentration range 0 Յ x Յ 1, the wurtzite in the range 0.375Յ x Յ 1 and the hexagonal structure over the range 0 Յ x Յ 0.5.…”

“…We have thus reported that AlN molar fractions of up to ϳ60% can be dissolved into c-Sc 1−x Al x N͑111͒, epitaxially deposited onto a ScN͑111͒ seed layer. 20 Higher AlN contents result in phase separation into wurtzite structure ͑w͒-AlN or AlN-rich w-Sc 1−x Al x N, with up to four epitaxial relationships to the seed layer. Akiyama et al reported on textured Sc 1−x Al x N thin films, with 0.54Յ x Յ 1, deposited by reactive rf dual-magnetron sputtering onto Si͑001͒ substrates.…”

“…The magnetron sputter epitaxy ͑MSE͒ deposition technique is employed, starting from optimal conditions for growing w-AlN and performing experiments with an increasing ScN concentration until the transformation to the cubic phase like in Ref. 20 is observed. The as-deposited films are characterized using a combination of ion beam analysis, x-ray diffraction ͑XRD͒, and electron microscopy techniques.…”

Preparation of scandium aluminum nitride thin films by using scandium aluminum alloy sputtering target and design of experiments

“…Thus the importance of the two control factors is not statistically accepted. Journal of the Ceramic Society of Japan 118 [12] 1166-1169 2010…”

YxAl1−xN thin films

“…For the (S)TEM-EDX measurements, a ~3 Å electron probe was used. [25,26], the presented alloys display considerably higher mixing enthalpies. Since Sc and Y share a similar electronic bonding behaviour, the larger volume difference between YN and AlN as compared to that between ScN and AlN is likely to be the major contributor to this finding.…”