Rhombohedral symmetry in GaAs_1−xN_x nanostructures

Nanocrystalline structures of GaAs_1−xN_x thin films were prepared on 7059 Corning glass substrates by means of an RF magnetron sputtering system using a GaAs target and N₂ as ambient-gas, at several values of substrate temperature (T _s). The range of T _s was chosen from room temperature to 400 °C. The nitrogen concentration into the GaAsN layers is (1.0% ± 0.2%). The average energy band gap of the GaAsN nanostructures, calculated from their optical absorption spectra, is 2.9 ± 0.2 eV. The Raman scattering spectra exhibit vibrational modes associated to the rhombohedral phase due to the crystalline structural transformation from the zincblende (ZB)-GaAs caused by the introduction of N into the lattice. From x-ray diffraction (XRD) patterns the ZB structure was identified with two additional pairs of peaks which were associated to two types of cubic to rhombohedral crystalline phase changes of the material. One type has a low deformation to a moderately elongated unit cell, and the second type has a higher deformation to a more elongated unit cell. The rhombohedral symmetry of the crystalline lattice in the GaAsN nanostructures has been calculated from XRD data to confirm experimental evidences. The total average grain size was determined from the Scherrer formula: 3.3 ± 1.2 nm. The photoluminescence spectra are characterized by a very broad emission band which encompasses photon energies from near infrared to UV (775–310 nm, i.e. 1.6–4.0 eV). (paper)