Nitrogen induced optical phonon shift in GaN_yAs_1-y studied by Raman Scattering

Abstract

We present a Raman study of pseudomorphically strained epitaxial films of the ternary alloy GaN_yAs_1-y grown on GaAs(100) with y ranging from 0 to 0.06. The optical phonon Raman spectrum of the alloy displays a two-mode behavior. The GaAs-like first order modes for y = 0.06 are represented by the strong longitudinal optic (LO1) mode at 287.4 cm⁻¹ and the weaker transverse optic (TO₁) mode at 269.0 cm⁻¹, while the GaN-like LO₂mode is observed at 475.6 cm⁻¹. Two very broad disorder-induced acoustic bands are evident at 80 and 170 cm⁻¹ due to atomic disorder within the crystalline network. Raman studies show that as the nitrogen concentration in the alloy increases, the GaAs-like LO₁band shifts linearly towards lower wavenumber while the linearly increasing GaN-like LO₂ phonon band deviates from linearity at higher nitrogen concentration (y ≥ 0.03). The reason for the deviation of the LO₂ phonon from linearity is discussed.