Magnetic Properties of Uniformly Ce-Doped Si Thin Films with n-Type Conduction

Abstract

Magnetic properties and the chemical bonding state of Ce for a diluted magnetic semiconductor (DMS), n-type Si:Ce thin films with a Ce concentration below 8.0 at. % grown by low-temperature molecular beam epitaxy (LT-MBE) are investigated. LT growth enables the films to have a uniform distribution of Ce in epitaxial Si films with a Ce concentration up to 8.0 at. %. The precipitation of the second phase, such as cerium silicide, is not recognized in the film with a Ce concentration of 4.0 at. % by electron diffraction using transmission electron microscopy (TEM) analysis. All the films exhibit n-type conduction. The electron density increases with increasing Ce concentration up to 0.07 at. % because of the generation of electrons by point defects. Then, the density decreases with increasing Ce concentration up to 1.1 at. % because of the compensation by the hole generated by substitutionally dissolved Ce3+. A positive magnetization due to a Ce3+ ion is observed in all the films. Unlike p-type Si:Ce, however, ferromagnetic or super-paramagnetic behavior is not observed in uniformly Ce-doped Si films with n-type conduction, suggesting that the hole plays an important role in the anomaly observed in magnetotransport behaviors in Ce-doped Si films.