Atomic and electronic structure of ultrathin fluoride barrier layers at the oxide/Siinterface

Abstract

A SrF2 ultrathin barrier layer on Si(001) is used to form a sharp interface andblock reactivity and intermixing between the semiconductor and aYb2O3 overlayer.Yb2O3/Si(001) andYb2O3/SrF2/Si(001) interfaces grown in ultra high vacuum by molecular beam epitaxy are studied byphotoemission and x-ray absorption fine structure. Without the fluoride interlayer,Yb2O3/Si(001) presents an interface reacted region formed bySiOx and/or silicate compounds, which is about 9 Å thick and increases up to 14–15 Å after annealing at 500–700 °C. A uniformsingle layer of SrF2 molecules blocks intermixing and reduces the oxidized Si region to 2.4 Å after deposition and to 3.5 Å afterannealing at 500 °C. In both cases we estimate a conduction band offset and a valence band offset of ∼ 1.7 eVand 2.4 eV between the oxide and Si, respectively. X-ray absorption fine structure measurements at theYb LIII edge suggest that the Yb oxide films exhibit a significant degree of static disorder with andwithout the fluoride barrier. Sr K edge measurements indicate that the ultrathin fluoridefilms are reacted, with the formation of bonds between Si and Sr; the Sr–Sr and Sr–Finteratomic distances in the ultrathin fluoride barrier film are relaxed to the bulk value.