Effect of thickness on the structural and optical properties of GaN films grown on Si(111)

GaN films with different thicknesses were grown on Si(111) substrates by Plasma-Assisted Molecular Beam Epitaxy (PA-MBE). The optical properties of the films were investigated using spectrophotometric measurements of the reflectance in the wavelength range 200-3,300 nm. With increasing film thickness, the refractive index (n) increased slightly, while the optical energy gap (E-g) changed with no specific trend. The structural properties of the grown films were studied at (002) reflections using two types of rocking curve measurements; normal rocking curve (omega-scan) and triple axis rocking curve (omega/2 theta-scan). The Full Width at Half Maximum (FWHM) of rocking curve decreased with increasing film thickness. Hall effect measurements showed that all the samples were n-type with carrier concentrations decreasing from 8.025 x 10(18) to 5.65 x 10(17) cm(-3), and mobility increasing from 14 to 110 cm(2) V-1 s(-1) as increasing the film thickness from 590 to 1,420 nm, respectively. Photoluminescence (PL) spectra for the grown GaN films with different thicknesses were measured at room temperature. PL spectra for all the samples exhibited band edge (BE) emissions at peak energies of 3.24 eV, with peak intensities increased with increasing the film thickness.