Electrical and optical properties of Fe doped AlGaN grown by molecular beam epitaxy

Electrical and optical properties of AlGaN grown by molecular beam epitaxy were studied in the Al composition range 15%–45%. Undoped films were semi-insulating, with the Fermi level pinned near Ec-0.6–0.7 eV. Si doping to (5–7)×1017 cm−3 rendered the 15% Al films conducting n-type, but a large portion of the donors were relatively deep (activation energy 95 meV), with a 0.15 eV barrier for capture of electrons giving rise to strong persistent photoconductivity (PPC) effects. The optical threshold of this effect was ∼1 eV. Doping with Fe to a concentration of ∼1017 cm−3 led to decrease in concentration of uncompensated donors, suggesting compensation by Fe acceptors. Addition of Fe strongly suppressed the formation of PPC-active centers in favor of ordinary shallow donors. For higher Al compositions, Si doping of (5–7)×1017 cm−3 did not lead to n-type conductivity. Fe doping shifted the bandedge luminescence by 25–50 meV depending on Al composition. The dominant defect band in microcathodoluminescence spectra was the blue band near 3 eV, with the energy weakly dependent on composition.