Indium Distribution within InxGa1?xN Epitaxial Layers: A Combined Resonant Raman Scattering and Rutherford Backscattering Study

Abstract

We report a Raman spectroscopy study performed at room temperature on In x Ga 1--x N epitaxial layers grown by metalorganic chemical vapour deposition on top of GaN/sapphire (0001) substrates. Resonant Raman measurements have been performed using excitation energies of 2.34, 2.54 and 3.02 eV. A shift of the A 1 (LO) phonon mode frequency was observed under different excitation energies. This is interpreted with respect to the composition and strain variations within the sample. The A 1 (LO) phonon line shape is analysed using a Spatial Correlation Model (SC). The structural parameters were determined by Rutherford backscattering spectrometry (RBS). IntroductionThe In x Ga 1--x N material system has played a considerable role in the development of light emitting devices operating in the visible spectral region [1].Raman spectroscopy has proven to be an informative tool in the investigation of semiconductors with the wurtzite (WZ) crystal structure. For the case of the In x Ga 1--x N alloy, it has been theoretically [2] and experimentally [3][4][5][6] demonstrated that it shows one-mode behavior, i.e. exhibits only one set of longitudinal optical (LO) and transverse optical (TO) phonons, whose frequencies vary almost linearly with compositional changes. Due to the lack of good quality samples for a wide range of composition, the A 1 (LO) phonon frequency dependence on the indium content x is not yet well-established and different behaviors can be found in the literature [4][5][6]. In some cases the observed asymmetrical band shape leads to an uncertainty on the phonon frequency at the Brillouin center zone. Furthermore, the state of strain of the samples is not always properly taken into account.In this work, we study an InGaN sample by RBS and resonant Raman scattering measurements. The low energy tail associated with the A 1 (LO) phonon line shape is analysed using the Spatial Correlation Model (SC) [7]. The Raman scattering enhancement is discussed assuming that resonance is achieved when the excitation energy is nearly the band gap E g .