UV Raman Study of A1(LO) and E2 Phonons in InGaN Alloys Grown by Metal-Organic Chemical Vapor Deposition on (0001) Sapphire Substrates

Abstract

ABSTRACTWe report on UV Raman spectroscopy of InxGa1−xN thin films grown on (0001) sapphire substrates using a specially designed metal-organic chemical vapor deposition (MOCVD) reactor. Eight films were examined in the compositional range 0<×<0.50. Mid and deep-UV Raman spectroscopy was done with the 325.2 nm line of the HeCd laser and the 244 nm line of a double frequency Ar ion laser. The mode behavior of the A1(LO) and E2 phonons was also investigated. We have found compelling evidence for one-mode behavior for the A1(LO) phonon mode, while our data for the E2 mode deviates from the predictions for one-mode behavior. The results for the A1(LO) mode are consistent with the previously reported phonon mode behavior in AlGaN alloys. Also, evidence regarding the presence of compositional inhomogeneities and spinodal decomposition in InGaN thin films is presented.