N-type doping of BaSi2 epitaxial films by arsenic ion implantation through a dose-dependent carrier generation mechanism

•As doping of BaSi2 epitaxial films by ion implantation and thermal annealing is studied.•An altered layer is found to form around the surface with a high dose of 1.0 × 1015 cm− 2.•The altered layer contains O atoms.•The altered layer brings about a high electron density exceeding the As dose.•Without the altered layer, highest possible electron density is less than 2 × 1017 cm− 3.

Arsenic doping by ion implantation and thermal annealing of the BaSi2 epitaxial films grown on Si(111) substrates has been studied. Raman spectroscopy shows that a structural change can occur by annealing at 500 °C after As implantation with as high dose as 1.0 × 1015 cm− 2. This structural change is shown to result in the formation of an altered layer after annealing at the surface by cross-sectional scanning electron microscopy. Secondary ion mass spectroscopy reveals that the altered layer contains a significant amount of O atoms. With the altered layer present, average electron density up to 6.0 × 1019 cm− 3 has been realized, which is revealed by the Hall measurement. On the other hand, without the altered layer, high resistance of the BaSi2 layer prevented the electrical characterization. Current path is discussed by theoretically calculating the band alignment and resistance, and possible highest electron density without the altered layer is extracted to be less than 2 × 1017 cm− 3.