Effects of Ba-to-Si deposition rate ratios on the electrical and photoresponse properties of arsenic-doped n-type BaSi2 films

Abstract

The formation of high-quality impurity-doped n-type BaSi2 films is inevitable for their use in solar cell applications. We grew arsenic (As)-doped n-type BaSi2 epitaxial films by molecular beam epitaxy with Ba-to-Si deposition rate ratios (RBa/RSi) varied in the range 0.8−3.9, and investigated their effect on the electrical and photoresponse properties of grown films. As-doped BaSi2 films showed n-type conductivity with an electron concentration of the order of 1016 cm−3 at room temperature regardless of the RBa/RSi. The full-width at half maximum of an Ag mode Raman peak (∼490 cm−1) decreased for samples grown under Si-rich conditions. This result indicates the decrease in Si vacancies acting as recombination centers in BaSi2 since this Raman peak position is close to that caused by Si vacancies. This is consistent with the result that the photoresponsivity reached a maximum in BaSi2 films prepared under Si rich conditions (RBa/RSi = 1.3). However, further Si-rich conditions (RBa/RSi = 0.8) led to the degradation of photoresponsivity. Photoluminescence spectra showed that the position of localized states changed depending on RBa/RSi, indicating that the type of defects changed in the BaSi2 films.