Formation and Transport of Polarons in β-Ga2O3: an Ab Initio Study

We investigated the formation of small-hole polarons in β-Ga₂O₃ from first-principles, accounting for their coupling to all phonon modes. Our results reveal that small-hole polarons can form at multiple oxygen sites, namely, O_I, O_II, and O_III, with the O_II site being the most stable. The phonons involved in the coupling for polaron formation at these three oxygen sites exhibit minimal differences. However, at the O_II site, the localized hole originates from entire highest valence band (EHVB), whereas at the O_I and O_III sites, the localized hole state is a hybridization of the EHVB and lower-lying bands. This distinction results in the lower contribution of electronic weight of small hole polarons on the O_II site, which leads the lowest formation energy for the polaron at this site. The hopping of small-hole polarons between O_II sites occurs via an adiabatic process, with an activation energy of 0.37 eV. Additionally, we investigated electron polarons in β-Ga₂O₃ using the same approach but observed no evidence of polaronic states, either large or small. This study provides new insights into polaron physics in β-Ga₂O₃ and offers guidance for understanding and exploring polarons in related materials.