Optical properties of scandium-doped aluminum nitride thin film for integrated photonics

Scandium (Sc)-doped aluminum nitride (AlN) has been widely used as a piezoelectric material in Micro-Electromechanical Systems (MEMS) devices. Recently, it also draws interests in photonics research contributed by its enhanced nonlinear optical property. Here, we report the (n, k) values of Sc-doped AlN thin films under various doping concentrations. These thin films with thickness of around 500 nm are deposited on silica through co-sputtering process. Reduced optical bandgap energies are observed at higher Sc doping concentrations. Furthermore, the top surface roughness of < 1 nm has been obtained through atomic force microscopy (AFM) measurement for the 30% Sc-doped AlN film in a 1 × 1 μm² region. Also, with etching process optimization, the 10% Sc-doped photonic waveguide sidewall angle and roughness have been obtained as ⪆80° and ⪅ 5 nm, respectively. Additionally, the patterned microring cavity has been characterized, with estimated intrinsic Q of 5.54×10⁴ . The reported results here pave the way towards Sc-doped AlN for integrated photonics, with potential applications in communication, sensing, and quantum computing.