Intrinsic origins of broad luminescence in melt-grown ZnGa2O4 single crystals

This work explores the luminescence properties of melt-grown ${\mathrm{ZnGa}}_2{\mathrm{O}}_4$ single crystals using photoluminescence spectroscopy and first-principles calculations. The photoluminescence spectra consist of numerous overlapping broad bands in the spectral range between 1.4 and 3.9 eV, which can be divided into low- (1.4–2.7 eV) and high-energy (2.7–3.9 eV) parts. When using below-gap excitation, the photoluminescence spectrum shows distinct orange and ultraviolet luminescence bands peaking at 1.99 and 3.36 eV, respectively. The results are interpreted by using configuration coordinate diagrams derived from hybrid functional calculations for self-trapped holes, as well as for the most stable native defects and their complexes. The calculations show that self-trapped holes, Zn antisites, and Zn-Ga antisite pairs give rise to strongly overlapping luminescence lines that are compatible with the high-energy side of the broad emission. For the low-energy side, we suggest Zn vacancies and their complexes with Ga antisites as potential intrinsic origins. The calculated Zn vacancy lineshape fits well with the orange luminescence band. Ga vacancies are unlikely to be the origin of the observed visible and ultraviolet emission, as the calculated luminescence lines occur in the infrared region. Moreover, complexes between the Ga vacancy and one or two Ga antisites, which would show luminescence at higher energies, are only metastable. It is more favorable for a Ga antisite to jump into the Ga vacancy, replacing the Ga antisite and vacancy with a Zn vacancy.