Study of beryllium acceptor states in aluminum nitride via cathodoluminescence analysis

We report a comprehensive study of beryllium (Be) acceptor states in aluminum nitride (AlN) using steady-state cathodoluminescence (CL) spectroscopy. A sharp emission is observed at 6.077 eV and attributed to the neutral Be-bound exciton (Be0X), with a corresponding binding energy of 44 meV. Two additional lower-energy peaks are identified as the first and second longitudinal optical phonon replicas of the Be0X transition. Temperature-dependent CL measurements reveal thermal quenching of the Be0X emission, with activation energies of 8.8 and 67 meV that correspond to exciton delocalization and effective quenching barrier, respectively. The free exciton transition energy in Be-doped AlN is consistent with a ∼90 meV bandgap blue shift relative to literature, attributed to biaxial compressive strain confirmed by XRD. Although instrumental error and sample charging in AlN make sub-nanometer precision in peak position difficult, the observed energy difference remains in reasonable agreement with strain-based calculations. This work demonstrates the feasibility of Be incorporation via ion implantation in AlN and presents direct optical evidence of Be-related acceptor states in AlN, offering insight into p-type doping strategies for ultrawide-bandgap semiconductors.