Compensation of Shallow Donors by Gallium Vacancies in Monoclinicβ-Ga2O3

Knowledge of the origin of deep levels and their impact on electrical properties is critical for device applications of ,B-Ga2O3. By annealing under an oxygen (O2) atmosphere, the resistivity in shallowdonor (zirconium) doped ,B-Ga2O3:Zr single crystals is found to increase by more than 10 orders of magnitude to (7 ? 4) ? 1010 S2 cm, which is comparable to the resistivity achieved by iron (Fe) acceptor doping of (5 ? 3) ? 1011 S2 cm. We combine thermoelectric effect spectroscopy and positron annihilation spectroscopy (PAS), which are sensitive to deep levels and concentration of open-volume defects, with modeling of the electrical properties, to study these strongly compensated crystals. We find the compensating level in the O2-annealed ,B-Ga2O3:Zr sample to be located at (0.727 ? 0.021) eV (E 2*) below the conduction band, which correlates with a vacancy signal from PAS data. The defect is most likely the relaxed split Ga vacancy ViGa, rather than a simple gallium vacancy, considering theoretical predictions of a small energy barrier to relax. We observe that, due to the unique nature of these vacancies and anisotropy in the monoclinic lattice, the Doppler-broadening parameter is rather small compared with other widegap compounds, and in such a case the positron diffusion length is a suitable parameter to estimate the open-volume defect concentration.

Automated summary

The study reveals the existence of a compensating level below the conduction band in the O2-annealed B-Ga2O3:Zr sample, possibly caused by the relaxed split Ga vacancy. The sample shows a significant increase in resistivity after annealing under oxygen atmosphere, and also exhibits unique vacancy characteristics and anisotropy in the monoclinic lattice.