  Here, we compare the material quality of AlxIn1-xN layers deposited on Si
with different crystallographic orientations, (100) and (111), via
radio-frequency (RF) sputtering. To modulate their Al content, the Al RF power
was varied from 0 to 225 W, whereas the In RF power and deposition temperature
were fixed at 30 W and 300oC, respectively. X-ray diffraction measurements
reveal a c-axis-oriented wurtzite structure with no phase separation regardless
of the Al content (x = 0-0.50), which increases with the Al power supply. The
surface morphology of the AlxIn1-xN layers improves with increasing Al content
and it is similar for samples grown on both Si substrates (the root-mean-square
roughness decreases from 12 nm to 2.5 nm). Furthermore, from TEM images we
notice a similar grain-like columnar morphology and defect density on samples
deposited on both Si substrates under the same conditions. Simultaneously grown
AlxIn1-xN-on-sapphire samples point to a residual n-type carrier concentration
in the 1020-1021 cm-3 range. The optical band gap energy of these layers
evolves from 1.75 eV to 2.56 eV with increasing Al content, consistent with the
blue shift of their low-temperature photoluminescence. In general, the material
quality of the AlxIn1-xN films on Si is similar for both crystallographic
orientations. Nonetheless, samples deposited on sapphire show an improved
structural and morphological characteristic likely due to the lower difference
in lattice constants between the nitride and the sapphire substrate.
