Valence band structure of AlN probed by photoluminescence

Deep ultraviolet photoluminescence (PL) was employed to probe the valence band structure of AlN epilayers grown by metal organic chemical vapor deposition on c-plane sapphire substrates. At 10 K, in addition to the dominant emission peak at 6.050 eV polarized in the E parallel to c direction, we observed two additional emission peaks at 6.249 and 6.262 eV polarized in the E perpendicular to c direction. These two emission lines are assigned to the recombination of free excitons related to the B and C valence bands. A more comprehensive picture of the valence band structure of AlN is thus directly obtained from the PL measurements.