  We report the first investigation on continuous-wave Raman lasing in
high-quality-factor aluminum nitride (AlN) microring resonators. Although
wurtzite AlN is known to exhibit six Raman-active phonons, single-mode Raman
lasing with low threshold and high slope efficiency is demonstrated. Selective
excitation of A$_1^\mathrm{TO}$ and E$_2^\mathrm{high}$ phonons with Raman
shifts of $\sim$612 and 660 cm$^{-1}$ is observed by adjusting the polarization
of the pump light. A theoretical analysis of Raman scattering efficiency within
${c}$-plane (0001) of AlN is carried out to help account for the observed
lasing behavior. Bidirectional lasing is experimentally confirmed as a result
of symmetric Raman gain in micro-scale waveguides. Furthermore, second-order
Raman lasing with unparalleled output power of $\sim$11.3 mW is obtained, which
offers the capability to yield higher order Raman lasers for mid-infrared
applications.
