Percolation-based vibrational picture to estimate nonrandom N substitution in GaAsN alloys

The number of N atoms in N-rich regions mostly due to nonrandom N incorporation in GaAsN (N∼4%), referred to as the $Nr$ rate, is studied using a nonstandard Raman setup that addresses transverse symmetry. The Ga–N optical range shows a two-mode signal which discriminates between the N-poor $(Np)$ and N-rich $(Nr)$ regions. This is discussed via a percolation-based picture for Be-chalcogenide alloys, which exhibit mechanical contrast with regard to the shear modulus. This applies to GaAs–GaN even though the contrast is in the bulk modulus. The balance of $Nr/Np$ strength provides a $Nr$ rate of ∼30%, i.e., much larger than the corresponding Be rate of ∼4% in random Be-based alloys.