The structure of low-index surfaces of β-Ga2O3

The physical and electronic structure of the (1 0 0), (0 1 0), (0 0 1) and (101¯) faces of β-Ga2O3 are addressed using ab initio theory. Restricted Hartree-Fock calculations, with large-core Ga and O pseudopotentials, are done to optimize the structure of first the bulk and then of slabs “cut” in the required orientations. The slab unit cells are fully relaxed during optimization, and the displacements of all atoms from the ideally-terminated positions are obtained as functions of depth into the bulk. For the relaxed slabs, single-point density functional theory calculations using the B3LYP functional and all-electron basis sets are performed to obtain surface energies, ionic charges and bond overlap populations. All surfaces exhibit a decrease in surface energy upon relaxation, and the local bonding at the surface is analyzed by comparing nearest-neighbor bond lengths and overlap populations with those in the bulk. The (101¯) surface, which exhibits a high energy when ideally terminated, undergoes large displacements and changes in bonding during relaxation leading to a substantial lowering of the surface energy. The band structure is also obtained for the lowest-energy surface, which is one of the possible non-polar terminations of the (1 0 0). The results provide insight into the growth and structure of β-Ga2O3 nanoribbons.