Abstract
Gallium oxide when doped with Mg becomes semi-insulating and can be useful for power electronic devices. The present work investigates optical transitions of neutral Mg (MgGa0) using photoinduced electron paramagnetic resonance spectroscopy, a variation of the traditional optical absorption. Steady-state and time-dependent measurements are carried out at 130 K by illuminating the samples with photon energies from 0.7 to 4.4 eV. Interpretation of the data using a model that incorporates electron–phonon coupling yields a defect transition level that is consistent with the MgGa−/0 level obtained from hybrid density functional theory calculations. We conclude that the neutral to negative transition of MgGa that we observe involves an electron transition from the valence band to the defect, and the MgGa−/0 level is located 1.2 eV above the valence band maximum, with a relaxation energy of 1.3 eV.
Highlights
The availability of potentially inexpensive, high quality, large single-crystalline substrates grown by melt growth methods such as floating zone (FZ), Czochralski (Cz), and edgedefined film-fed growth (EFG) enhances the potential of gallium oxide technologies
We show that by incorporating electron–phonon coupling when fitting our experimentally determined optical cross-section spectrum, we extract a value for a defect level that is consistent with the Mg−G/a0 level calculated using density functional theory (DFT)
We show that the transition level (TTL) and relaxation energies extracted from a best fit of a cross-section model to our optical crosssection data agree well with the DFT-predicted TTL and relaxation energies for the Mg−G/a0 transition
Summary
Gallium oxide (β-Ga2O3) is a promising ultrawide-bandgap semiconductor for power electronics due to its larger bandgap (∼4.9 eV) and higher estimated breakdown field (8 MV/cm) compared to the present counterparts such as SiC and GaN. Gallium oxide holds promise for applications in solar blind photodetectors because of its high transparency in the ultraviolet wavelength region. the availability of potentially inexpensive, high quality, large single-crystalline substrates grown by melt growth methods such as floating zone (FZ), Czochralski (Cz), and edgedefined film-fed growth (EFG) enhances the potential of gallium oxide technologies. For the successful engineering of Ga2O3-based devices, it is critical to have a thorough understanding and control of defects and doping of this material. By studying the thermal decay of neutral Mg acceptors in Mg-doped Ga2O3, Lenyk et al suggested that the Mg−G/a0 level is ∼0.65 eV above the VBM.. By studying the thermal decay of neutral Mg acceptors in Mg-doped Ga2O3, Lenyk et al suggested that the Mg−G/a0 level is ∼0.65 eV above the VBM.13 This latest experimental report of the MgG−/a0 level questions the validity of the previously reported experimental and theoretical values. The measured spectrum is compared to a model proposed by Pässler, which incorporates electron–phonon coupling, and has previously been used to interpret the optical absorption of deep level defects in SiC, GaN, and Ga2O3.19–21 We use first-principles hybrid DFT calculations to determine the configuration coordinate diagram for the optical absorption of holes from the VBM into MgG−/a0. We show that by incorporating electron–phonon coupling when fitting our experimentally determined optical cross-section spectrum, we extract a value for a defect level that is consistent with the Mg−G/a0 level calculated using DFT
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