Formation and Transport of Polarons in β-Ga₂O₃: an <i>Ab Initio</i> 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, OI, OII, and OIII, with the OII 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 OII site, the localized hole originates from entire highest valence band (EHVB), whereas at the OI and OIII 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 OII site, which leads the lowest formation energy for the polaron at this site. The hopping of small-hole polarons between OII 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.