Aluminium nitride integrated photonics: a review

Integrated photonics based on silicon has drawn a lot of interests, since it is able to provide compact solution for functional devices, and its fabrication process is compatible with the mature complementary metal-oxide-semiconductor (CMOS) fabrication technology. In the meanwhile, silicon material itself has a few limitations, including an indirect bandgap of 1.1 eV, transparency wavelength of >1.1 μm, and insignificant second-order nonlinear optical property. Aluminum nitride (AlN), as a CMOS-compatible material, can overcome these limitations. It has a wide bandgap of 6.2 eV, a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect. Furthermore, it also exhibits piezoelectric and pyroelectric effects, which enable it to be utilized for optomechanical devices and pyroelectric photodetectors, respectively. In this review, the recent research works on integrated AlN photonics in the past decade have been summarized. The related material properties of AlN have been covered. After that, the demonstrated functional devices, including linear optical devices, optomechanical devices, emitters, photodetectors, metasurfaces, and nonlinear optical devices, are presented. Last but not the least, the summary and future outlook for the AlN-based integrated photonics are provided.