Excited states ofFe3+in GaN

We report a comprehensive photoluminescence excitation (PLE) investigation of the deep iron acceptor in hexagonal GaN. PLE spectra of the ${\mathrm{Fe}}^{3+}$ ${[}^4$ ${\mathrm{T}}_1$ (G)${\mathrm{-}}^6$ ${\mathrm{A}}_1$ (S)] luminescence in semi-insulating GaN samples reveal intracenter excitation processes via excited states of the ${\mathrm{Fe}}^{3+}$ center. Zero-phonon lines resolved around 2.01 and at 2.731 eV are attributed to the ${}_{}{}^6{}_{}{}^{}$ ${\mathrm{A}}_1$ (S)${\mathrm{-}}^4$ ${\mathrm{T}}_2$ (G) and the ${}_{}{}^6{}_{}{}^{}$ ${\mathrm{A}}_1$ (S)${\mathrm{-}}^4$ E(G) transition, respectively. A steplike excitation structure on the low-energy onset of the ${\mathrm{Fe}}^{3+\mathrm{/}2+}$ charge-transfer band is attributed to the formation of a (${\mathrm{Fe}}^{3+}$,e,h) complex at 2.888 eV. We estimate a binding energy of 280 meV locating the deep ${\mathrm{Fe}}^{3+\mathrm{/}2+}$ acceptor level 3.17 eV above the valence-band maximum. In n-type GaN samples the ${\mathrm{Fe}}^{3+}$ luminescence is excited by hole-transfer processes. The experimental results indicate that the internal reference rule fails for the GaN/GaAs heterostructure.