  The existing silicon-carbide-on-insulator photonic platform utilizes a thin
layer of silicon dioxide under silicon carbide to provide optical confinement
and mode isolation. Here, we replace the underneath silicon dioxide layer with
a 1-$\mu$m-thick aluminum nitride and demonstrate a
4H-silicon-carbide-on-aluminum-nitride integrated photonics platform for the
first time. Efficient grating couplers, low-loss waveguides, and compact
microring resonators with intrinsic quality factors up to 210,000 are
fabricated. In addition, by undercutting the aluminum nitride layer, the
intrinsic quality factor of the silicon carbide microring is improved by nearly
one order of magnitude (1.8 million). Finally, an optical pump-probe method is
developed to measure the thermal conductivity of the aluminum nitride layer,
which is estimated to be over 30 times of that of silicon dioxide.
