Computational study of positron annihilation parameters for cation mono-vacancies and vacancy complexes in nitride...

We calculate positron annihilation parameters, namely the S and W parameters from the Doppler broadening spectroscopy and the positron lifetime [Formula: see text], for defect-free states as well as cation mono-vacancies and vacancy complexes in nitride semiconductor alloys Al_0.5Ga_0.5N, In_0.5Ga_0.5N and Al_0.5In_0.5N. The obtained distributions of these parameters differ from compound to compound. Especially, the S-W relation for In_0.5Ga_0.5N is very different from that for Al_0.5Ga_0.5N. For the cation mono-vacancies, introducing local structural parameters, their correlations with S, W and [Formula: see text] are investigated. The S and [Formula: see text] variations are well described with the size distributions of the vacancies while the W variation is related to the presence of localized d electrons. For the vacancy complexes as well as the cation mono-vacancies, multiple-linear-regression models to describe S, W and [Formula: see text] are successfully constructed using the local structural parameters as descriptors. The S-W and S-[Formula: see text] relations are also compared with those for AlN, GaN and InN.