Impact of Sc-doping on structural, phase purity, and dielectric properties of AlN thin films

Aluminum nitride (AlN) thin films were deposited using RF magnetron sputtering at 150 and 175 W to investigate the impact of sputtering power and scandium (Sc) doping on their structural, phase purity, and dielectric properties. X-ray diffraction analysis confirmed high c-axis orientation for films grown at 175 W (for Al), while x-ray photoelectron spectroscopy core spectra of Al and N elements revealed binding energies at 73.5 and 396.4 eV, respectively, verifying its oxidation state, which indicates the formation of AlN without any oxynitride. Atomic force microscopy substantiated that the film roughness was less than 3 nm, suitable for surface acoustic wave devices. The dielectric constant obtained through capacitance–voltage (C−V) measurements was found to be 7.17 for the optimized AlN film. Furthermore, AlScN thin films with different Sc concentrations were deposited by fixing the optimized Al power at 175 W and varying the Sc power at 60 (AlScN–60) and 90 W (AlScN−90). AlScN–60 exhibited a highly c-axis orientation and phase pure nature, while AlScN–90 showed the formation of unwanted scandium oxide, which was confirmed through x-ray photoelectron spectroscopy. Pristine AlN deposited at 175 W and AlScN–60 samples followed space charge limited conduction (SCLC) mechanism, whereas AlN deposited at 150 W and AlScN–90 exhibited both SCLC and Poole–Frenkel conduction mechanisms. The incorporation of Sc into AlN lattice results in an increase in the dielectric constant, while the leakage current significantly decreases.