Properties of GaN films deposited on Si(111) by radio-frequency-magnetron sputtering

GaN films have been deposited on Si(111) substrates by reactive rf-magnetron sputtering at nitrogen pressures from 0.08 to 2.70 Pa without intentionally heating the substrates. X-ray diffraction (XRD), spectroscopic ellipsometry (SE), and ex situ atomic-force microscopy (AFM) observations have been carried out. The XRD patterns indicate that the GaN films deposited at pressures lower than 1.10 Pa are polycrystalline films highly oriented with the (0001) plane preferred, while those deposited at ⩾1.10 Pa display mixed orientations or amorphous form. The pseudodielectric function ε(E)=ε1(E)+iε2(E) of the sputter-deposited GaN films has been measured by SE in the range between 1.50 and 5.00 eV at room temperature. The measured ε(E) spectra are analyzed by taking into account the effects of surface roughness based on an effective medium model. The roughness thickness for the film deposited at 0.27 Pa is determined to be ∼17 Å, which is comparable to the AFM rms value (∼11 Å).