Effects of a 50 nm AlN intermediate layer on the properties of Al1-xScxN films with varying Sc concentrations

This study fabricated Al_1-xSc_xN thin films with varying Sc doping concentrations on c-sapphire substrates using dual-target magnetron sputtering, and analyzed the impact of a 50-nm-thick AlN intermediate layer. By precisely adjusting the radio frequency power of the Sc target, films with doping concentrations ranging from 8 % to 32 % are obtained. The absence of the AlN intermediate layer, high Sc-doped films exhibit poor quality and significant phase separation on c-sapphire substrates. In contrast, upon the introduction of the intermediate layer, only the peak of the 0002 reflection of the wurtzite phase is manifested, accompanied by a remarkable enhancement in crystallinity and a substantial reduction in residual stress. X-ray photoelectron spectroscopy (XPS) analysis indicates that the intermediate layer strengthens the Sc-N bonds and reduces oxygen impurities. Optical characterizations reveal that the films containing this intermediate layer exhibit higher transmittance in the ultraviolet–visible region beyond the absorption edge, and their direct bandgap is closer to the theoretical value. This study verifies the crucial role of the AlN intermediate layer in optimizing the properties of Al_1-xSc_xN films. It provides some theoretical basis for the application of the AlScN/AlN/c-sapphire structure in devices such as high-performance radio-frequency filters and ultraviolet solar-blind detectors, which is conducive to enhancing the performance of these devices in relevant fields and expanding their functions.