Composition-dependent structural properties in ScGaN alloy films: A combined experimental and theoretical study

Experimental and theoretical results are presented regarding the incorporation of scandium into wurtzite GaN. Variation of the a and c lattice constants with Sc fraction in the low Sc concentration regime (0%-17%) are found that can be well explained by the predictions of first-principles theory. The calculations allow a statistical analysis of the variations of the bond lengths and bond angles as functions of Sc concentration. The results are compared to predictions from both a prior experimental study [Constantin, Phys. Rev. B 70, 193309 (2004)] and a prior theoretical study [Farrer and Bellaiche Phys. Rev. B 66, 201203(R) (2002)]. It is found that the ScGaN lattice can be very well modeled as being wurtzitelike but with local lattice distortions arising from the incorporation of the Sc atoms. Effects of the addition of Sc on the stacking order for a large Sc fraction is also studied by high resolution transmission electron microscopy. The results show the existence of stacking faults, and induced stacking disorder. The explanation for the lattice constant variations is based on the effects of local lattice distortions and not related to the stacking faults.