A set of AlN/Al xGa 1-xN (x ∼ 0.65) quantum wells (QWs) with well width L w, varying from 1 to 3 nm has been grown by metal organic chemical vapor deposition. Low temperature photoluminescence (PL) spectroscopy has been employed to study the L w dependence of the PL spectral peak position, emission efficiency, and linewidth. These results have shown that these AlN/AlGaN QW structures exhibit polarization fields of ∼4 MV/cm. Due to effects of quantum confinement and polarization fields, AlN/AlGaN QWs with L w between 2 and 2.5 nm exhibit the highest quantum efficiency. The dependence of the emission linewidth on L w yielded a linear relationship. The implications of our results on deep ultraviolet optoelectronic device applications are also discussed.