Towards B-doped p-BaSi2 films on Si substrates by co-sputtering of BaSi2, Ba, and B-doped Si targets

BaSi2 is one of the emerging materials for thin-film solar cell applications; hence the conductivity control by impurity doping is of great importance. The formation of B-doped p-BaSi2 films has been achieved by molecular beam epitaxy and vacuum evaporation. We fabricated B-doped BaSi2 films on Si substrates at 600 °C by co-sputtering BaSi2, Ba, and B-doped Si targets, followed by post-annealing at 900 °C or 1000 °C for 5 min in an Ar atmosphere. Contrary to expectations, as-grown sample and the sample annealed at 900 °C showed n-type conductivity, while the sample annealed at 1000 °C showed p-type conductivity. The reason for the n-type conductivity was discussed based on first-principles calculation considering the presence of oxygen atoms in the order of 1021 cm−3. The n-type conductivity for B-doped BaSi2 is possible only when both the B and O atoms being a substitution impurity are in the same Si4 tetrahedron.