Trapping of multiple H atoms at the Ga(1) vacancy in β-Ga₂O₃

Recent suggestions that hydrogen incorporation at the Ga(1) vacancy in β-Ga2O3 may have an impact on its electronic properties have led us to extend our earlier work on these defects. While our previous work provides strong evidence for one, two, and perhaps three or four H trapped into the shifted vacancy configurations introduced by Varley and Kyrtsos, the apparent experimental absence of several H trapped in the unshifted configuration is puzzling. While a structure of two hydrogen atoms trapped in the unshifted configuration is not favored energetically, structures of three or four hydrogens in the unshifted configuration are favored. We suggest that these structures are absent because there are no available pathways for the system to reach them by sequentially trapped H and, therefore, that three- or four-hydrogen defects will occur only in the shifted vacancy configurations.