Pulsed laser deposition of aluminum nitride thin films onto sapphire substrates

Abstract

The paper presents experimental study results of surface morphology and structural and optical properties of sapphire AlN films obtained by pulsed laser spraying. Method. Thin AlN films on sapphire were used as experimental samples. The preparation of AlN films was carried out using a combined installation of ion-beam and pulsed laser radiation. The deposition process was performed by sputtering a rotating aluminum target with 532 nm wavelength AYG: Nd3+ laser in the atmosphere of very pure nitrogen at the pressure of 3 and 4 Pa. The energy density of the laser pulse was 4 J/cm2 with a pulse duration of 15 ns and a pulse repetition rate of 15 Hz. The distance from the target surface to the sapphire substrate was 50 mm; the substrate temperature was 600 °C. Main Results. Using scanning electron microscopy and energy dispersive analysis, it was found that AlN films obtained at the nitrogen pressure in a vacuum chamber of 4 Pa have a composition more related to stoichiometric than AlN films obtained at the nitrogen pressure in a vacuum chamber of 3 Pa. The optical spectroscopy was used to study the transmission spectra of the samples under research. It was determined that the maximum transmission coefficient values of AlN films obtained at the nitrogen pressure in the vacuum chamber of 3 Pa (95.12 %) and 4 Pa (97.65 %) are within the wavelength range of 400–410 nm. The transmittance in the studied wavelength range of 300–1100 μm is at least 87 %, which characterizes the obtained film samples as optically transparent. Practical Relevance. The studied thin AlN films can be used as a buffer layer in optoelectronic devices, including the case of creating light-emitting diodes based on GaN and AlxGa1–xN of short-wave visible light and white-emitting devices