Al In N
Figure 3.31 shows the Al-composition dependence of XRD 2θ -ω scans around the (002)-plane of In1−xAlxN ternary alloys grown at 550◦C. It is shown that a single diffraction peak is observed in each In1−xAlxN alloy and the Al composition is monotonically shifted from the InN-rich to the AlN-rich side. The In1−xAlxN alloys are grown without apparent phase separation in the whole Al composition range. Figure 3.32 shows the Al composition dependence of the electron concentration and the FWHM values for several XRD characterizations for the In1−xAlxN alloys. The crystallinity tends to be poorer with increasing x up to ∼0.3, probably because of alloying effects between those materials having a large immiscibility gap, that is, InN and AlN. With increasing x above 0.3, however, the crystallinity tends to be improved, probably due to reduced lattice mismatch with the GaN template. The best crystalline In1−xAlxN is obtained at x = 0.77, which is close to the lattice matching composition (x = 0.82) to the GaN template. Further, as shown in Fig. 3.32, there is a strong correlation between the electron concentration and the crystallinity of the In1−xAlxN, that is, the carrier concentration tends to increase in poorer quality samples.