On the Origin of the 4.7 eV Absorption and 2.8 eV Emission Bands in Bulk AlN Substrates

One of the main limitations based on point defects in AlN is related to the UV absorption band present at 265 nm. This relatively broad absorption band limits the use of bulk substrates within the deep UV range and several complicated fabrication procedures have been devised to overcome this limitation. The origin for this absorption band along with corresponding photoluminescence signatures will be reviewed. C_N^- and V_N⁺ were identified as the point defects directly associated with the main absorption at 4.7 eV and the emission at 2.8 eV. The main absorption is due to a transition between the C_N^- state and conduction band, while the emission arises from a DAP transition between the donor V_N⁺ and acceptor C_N^- through the 4.7 eV excitation channel. New observations based on photoluminescence excitation are presented to further support the assignments previously made.