Electric field dependence of major electron trap emission in bulk β-Ga₂O₃: Poole-Frenkel effect versus phonon-assisted tunneling

Measurements of deep trap spectra in bulk β-Ga₂O₃ crystals showed the parameters of the two dominant centers with levels near Ec-0.8 eV (E2) and Ec-1 eV(E3) are affected the electric field during deep level transient spectroscopy (DLTS). Both DLTS spectra measurements of the emission rates of the E2 and E3 traps and measurements of emission rates as a function of electric field from capacitance decay curves obtained at a fixed temperature (380 K) show that, for strong electric field with magnitude above ∼5 × 10⁵ V.cm^-1, the emission rates of these traps increase with increasing field. For the E2 traps, the increase is driven by phonon assisted tunneling. This points to the trap being an acceptor, which is consistent with reported attribution of the center to substitutional Fe acceptors. For the E3 trap, the field dependence indicates the dominant mechanism is the Poole-Frenkel effect, operable for Coulombic centers. It is concluded that this commonly observed trap is a deep donor.