Influence of Ba-to-Si deposition rate ratios on the electrical and optical properties of B-doped BaSi2 epitaxial films

Abstract

BaSi2 is considered a candidate for a light absorbing layer of a solar cell. The carrier type, carrier density, and photoresponsivity of undoped BaSi2 films depend on Ba-to-Si deposition rate ratios (R Ba/R Si) during molecular beam epitaxy (MBE). In this study, we examined these properties of B-doped BaSi2 epitaxial films grown by MBE. We fabricated 0.5 μm thick lightly B-doped BaSi2 epitaxial films on Si (111) substrates at a substrate temperature of 600 C. R Ba/R Si was varied in the range 1.0-5.6. The B concentration was estimated to be 3 1016 cm-3. The p-type BaSi2 films were formed only in the range of R Ba/R Si = 2.0-2.9, whereas BaSi2 formed with other values of R Ba/R Si showed n-type conductivity. The photoresponsivity significantly depended on R Ba/R Si, and reached values higher than those obtained for undoped BaSi2 films. We ascribed the enhancement of photoresponsivity to B atoms making defects inactive in B-doped BaSi2 films.