| AVS 56th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF1-MoM |
| Session: | Thin Films: Growth and Characterization I |
| Presenter: | C. Höglund, Linköping University, Sweden |
| Authors: | C. Höglund, Linköping University, Sweden J. Bareño, Argonne National Laboratory J. Birch, Linköping University, Sweden B. Alling, Linköping University, Sweden Z. Czigány, Hungarian Academy of Sciences, Hungary L. Hultman, Linköping University, Sweden |
| Correspondent: | Click to Email |
Reactive magnetron sputter epitaxy was used to grow thin solid films of Sc1-xAlxN (0 ≤ x ≤ 1) onto ScN(111) and AlN(0001) seed layers at substrate temperatures of 600ºC and 800°C, respectively. The films were analyzed by Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA), x-ray diffraction (XRD) and transmission electron microscopy (TEM). RBS and ERDA showed that stoichiometric films were obtained in the entire composition range (molar fractions x = 0, 0.14, 0.29, 0.51, 0.73, 0.90, 1.0) using elemental Sc and Al targets and N2 as the reactive gas. TEM and XRD show that rocksalt structure (c) Sc1-xAlxN(111) solid solutions can be epitaxially grown onto the isostructural c-ScN(111) seed layers with AlN molar fractions up to x ~ 0.6 , whereafter the system phase separates into c- and wurtzite structure (w) Sc1-xAlxN. Upon phase separation, the w-domains are present in three different orientations relative to the seed layer, namely Sc1-xAlxN(0001) || ScN(111) with Sc1-xAlxN[-12-10] || ScN[1-10], Sc1-xAlxN(10-11) || ScN(111) with Sc1-xAlxN[-12-10] || ScN[1-10], and Sc1-xAlxN(10-11) || ScN(113). When growth was performed onto w-AlN(0001) seed layers, epitaxial w-Sc1-xAlxN(0001) with AlN molar fractions x in the range ~0.50 to 1.00 were obtained. For AlN molar fractions of 0.28 and less, the film formed an epitaxial c-Sc1-xAlxN(111) phase with double position domains.
The lattice parameter for the c-Sc1-xAlxN films closely followed the values predicted by first principles density functional theory calculations, only slightly deviating from Vegard’s law. On the contrary, the lattice parameters of the w-Sc1-xAlxN varied considerably less than predicted. Our calculated mixing enthalpies of c-, w-, and zinc blende Sc0.50Al0.50N solid solutions predict that the alloy is metastable with respect to phase separation for all temperatures below the melting points of AlN and ScN.