Peculiarities in the pressure dependence of photoluminescence in InAlN

Studies of ambient‐pressure and high‐pressure behavior of photoluminescence (PL) for series of In x Al 1− x N layers are presented. The measured evolution of PL energy ( E PL ) with x is characterized by a clear decrease of E PL and exhibits a strong bowing. This dependence corresponds to the predictions of ab initio calculations of the band‐gap energy changes E G with x . However, values of E PL are clearly lower than E G , for 0< x <0.3. For higher x , the measured E PL follows well the calculated E G . The experimentally determined pressure coefficient of PL energy (d E PL /d p ) shows a complicated behavior for alloys with different In‐content. We found a strong reduction of d E PL /d p for 0< x <0.3 and a relatively constant magnitude of this coefficient for higher x . Moreover, for the lower x region, we observed d E PL /d p that can differ even by a factor two in samples with nominally very similar In‐content. The general tendency in d E PL /d p evolution with x corresponds to lower values than calculated d E G /d p for alloys with non‐uniform indium distribution. We propose two not necessary independent explanations of these experimental findings. First, due to non‐uniform In distribution (induced, e.g. by defects or non‐homogeneous strain) both E PL and d E PL /d p are reduced. Second, a similar behavior results from an involvement of the localized states, whose formation and contribution to PL can be induced by strain and/or native defects. In both hypotheses, the strain/defect density can significantly change around x  ≈ 0.18 where In x Al 1− x N layers are lattice matched to GaN template.