Electrochemically sliced low loss AlGaN optical microresonators

High quality single crystal III-Nitride films are often formed over a thick buffer to reduce growth induced defects on a lattice mismatched substrate. However, it is challenging to fabricate nanophotonic waveguiding structures directly from this very top layer. Here, we demonstrate electrochemical slicing of high quality AlGaN thin films and its subsequent transfer to a lower index oxided silicon substrate for lithographic patterning of photonic waveguide and microresonators. TEM analysis of the nanomembrane waveguide demonstrates an AlGaN layer free of misfit dislocations commonly found in conventional epitaxial AlGaN grown on sapphire or Si. We probe the low material optical loss (1.22 dB/cm) of the nanomembrane by measuring the optical quality (Q) factor at 780 nm. High intrinsic quality factors of 680 000 are achieved after optimizing fabrication process. This versatile, low loss AlGaN device opens applications for nonlinear photonics at visible wavelengths.