Optical properties of aluminium nitride films obtained by pulsed laser deposition: an ellipsometric study

Aluminium nitride (AlN) films obtained by pulsed laser deposition (PLD) at different low ambient nitrogen pressure have been optically investigated by spectral ellipsometry within the 300-800 nm wavelength range, Sellmeier and Wemple-DiDomenico approximation approaches have been applied for the ellipsometric data analysis. Optical parameters such as refractive index and single oscillator energies of deposited films were estimated and their dependence on the N-2 pressure was studied. The obtained refractive index values of AlN films are around 2 in a wide wavelength region above 400 nm and suggest the growth of a polycrystalline structure. The relatively low (< 3.4 eV) threshold energies indicate the formation of a defective and disordered structure, formed during the deposition process.