Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride

Abstract

Photoluminescence (PL) spectroscopy is employed to determine the nature of a near-infrared PL emission with a no-phonon line at \ensuremath{\sim}0.88 eV, commonly present in electron-irradiated GaN. This PL emission is suggested to originate from an internal transition between a moderately shallow excited state (with an ionization energy \ensuremath{\sim}21 meV) and the deep ground state (with an ionization energy \ensuremath{\sim}900 meV) of a deep defect. The existence of a higher-lying second excited state related to the 0.88-eV PL center is also shown from temperature-dependent studies. A different electronic character of the wave functions related to the first and second excited states has been revealed by PL polarization measurements. Since the PL emission has been observed with comparable intensity in all electron-irradiated GaN samples independent of doping on the starting material, it is proposed that either native defects, or common residual contaminants or their complexes are involved. The substitutional ${\mathrm{O}}_{\mathrm{N}}$ donor (or related complex) is considered as the most probable candidate, based on the observed striking similarity in the local vibrational properties between the 0.88-eV PL centers and the substitutional ${\mathrm{O}}_{\mathrm{P}}$ donor in GaP.