Impact of Ba to Si deposition rate ratios during molecular beam epitaxy on carrier concentration and spectral response of BaSi2 epitaxial films

Undoped 0.5-mu m-thick BaSi2 epitaxial films were grown on Si(111) substrates with various ratios of the Ba deposition rate to the Si deposition rate (R-Ba/R-Si) ranging from 1.0 to 5.1, and their electrical and optical properties were characterized. The photoresponse spectra drastically changed as a function of R-Ba/R-Si, and the quantum efficiency reached a maximum at R-Ba/R-Si = 2.2. Hall measurements and capacitance versus voltage measurements revealed that the electron concentration drastically decreased as R-Ba/R-Si approached 2.2, and the BaSi2 films with R-Ba/R-Si = 2.0, 2.2, and 2.6 exhibited p-type conductivity. The lowest hole concentration of approximately 1 x 10(15) cm(-3) was obtained for the BaSi2 grown with R-Ba/R-Si = 2.2, which is the lowest value ever reported. First-principles calculations suggest that Si vacancies give rise to localized states within the bandgap of BaSi2 and therefore degrade the minority-carrier properties. Published by AIP Publishing.