Structural,optical and dispersion characteristics of nanocrystalline GaN films prepared by MOVPE

In this work, nanocrystalline GaN film was grown on a c-plane sapphire substrate by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties of the nanocrystalline GaN thin film were studied. The morphological and structural properties of GaN film were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. According to the X-ray diffraction spectrum, a GaN film was formed with a wurtzite structure, which is the stable phase. The optical parameters were determined using spectrophotometric measurements of transmittance and reflectance in the wavelength range 200–2500 nm. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals a direct allowed transition with a band gap of 3.34 eV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–Didomenico (WD) model. The single oscillator energy (E_o), the dispersion energy (E_d), the high frequency dielectric constant (ε_∞), the lattice dielectric constant (ε_L) and the free charge carrier concentration (N) were estimated. From the optical dielectric analysis, the optical conductivity, volume and surface energy loss functions were calculated. Moreover, the third-order nonlinear optical susceptibility χ⁽³⁾ was also considered.