Phonons and Valence-band Splitting in Strained GaAs_1-x N_x /GaAs Epilayers

—The strain effects in strained GaAs_1-xN_x epilayers are characterized by Raman spectroscopy and photocurrent spectra at various nitrogen composition. In addition, the nitrogen composition and the strain were determined by using high-resolution X-ray diffraction (HR-XRD). The Raman spectra are observed to be dominated by the GaAs-like longitudinal optical (LO) phonon mode as the strongest peaks show up around 289~294 cm^-1. Moreover, the weak and broad peaks features in the range of 255~276 cm^-1 originate from the peaks of GaAs-like transverse optical (TO) phonon mode and disorder induced, GaN-like LO. And the Raman peak shifts toward lower wave number with increasing nitrogen compositions, which is indicates the presence of tensile strain in the strained GaAs_1-xN_x epilayers. The valence-band splitting of GaAs_1-xN_x are obtained from photocurrent spectra. As the nitrogen concentration increases, the tensile strain in strained GaAs_1-xN_x epilayers increases while the valence-band splitting increases.