Low-loss AlN films grown on sapphire by high-temperature MOCVD

Single-crystal AlN-on-sapphire, possessing both a strong Kerr nonlinear effect and high-power handling as well as a very large band gap, is a fascinating platform for integrated optics. High-temperature metal-organic chemical vapor deposition of AlN films is attractive as an elevated temperature is believed to enhance both the crystalline quality and the deposition efficiency. In this contribution, we report the epitaxy and characterization of AlN-on-sapphire grown at 1400°C. The AlN films had much improved crystalline quality in terms of the dislocation density, XRD FWHM values, and AFM root-mean-square roughness. A fully etched MRR was fabricated with the standard i-line photolithography, and an intrinsic Q-factor of 5.1 × 10⁶ is achieved at the wavelength of 1553 nm in the TE polarization, indicating a low propagation loss of less than 0.073 dB/cm. Furthermore, efficient thermo-optic tuning was demonstrated with an integrated thermal heater, delivering a tuning efficiency of 0.65 pm/mW across one FSR while maintaining a high Q-factor above 4.1 × 10⁶.