Metal-Coated Zinc Oxide Nanocavities

We theoretically demonstrate that metals can be useful for increasing the quality factor and confinement factor of a zinc oxide (ZnO) nanocavity. For small cavities, the advantages of low radiation loss and significant mode confinement due to metal coating outweigh the disadvantage of absorption loss from metal and efficiently lower the threshold material gain. The performances of ZnO cavities without metal coating, with aluminum (Al) coating, and with silver (Ag) coating are investigated. The results indicate that while surface-wave-like plasmonic modes are lossy due to metal loss, the performances of well-confined dielectric modes are indeed improved significantly as a result of metal. Both Al and Ag can significantly reduce the threshold material gain of the uncoated ZnO cavity from 16 613 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to less than 5000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . In particular, the threshold material gain of Ag-coated cavity is reduced to only 3206 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> .