Abstract
We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.
Highlights
We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level
Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 Energy above VBM (eV) photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has been shown to occur in pure GaN samples
In this Letter, we present calculated formation and ionization energies of nitrogen vacancies (VN) and Mg substituting on a Ga site (MgGa) in GaN in the dilute limit, using a multiscale embedded cluster approach
Summary
560 410, 800 energies of photoexcited electrons recombining with these defect levels, as would be observed in PL experiments, where, after excitation, atoms typically do not have adequate time to fully relax. Our calculations are in excellent agreement with the low T and [Mg] PL spectra observed experimentally [16,17]. We reproduce well the DAP PL peaks at 3.21 and 3.27 eV, [36] and the ABE peak at 3.466 eV. The 2.75 eV IE of Mg−Ga, in approximate agreement with the observed BL peak, is unlikely to be observed due to its high formation energy (1.404 eV)
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