A study of the growth of Lu2O3 on Si(001) by synchrotron radiation photoemission and transmission electron microscopy

Rare earth oxides are among the materials which are presently studied as possible replacements of amorphous silicon dioxide as gate insulators in nanometric Si devices; in fact, they generally exhibit high values of the dielectric constant (“high-”), a necessary requirement to obtain a high capacitance with layer thickness greater than the value below which tunnelling currents become unacceptably high. Lu2O3 is one of the rare earth oxides which may have the required properties in view of its quite high values of k and forbidden band gap. Since the envisaged dielectric layers are only a few nm thick a description and a physical understanding of the atomic and electronic structure of the interface are of great importance. In this paper, we report a study by synchrotron radiation photoemission and transmission electron microscopy of the growth of Lu2O3 on Si(001). We provide evidence of a rather complex structure in which all silicon suboxides and SiO2 are present at the same time, along with a silicate – like phase and Lu2O3 itself; moreover, both crystalline and amorphous portions are present. The valence band discontinuity is found to be 3.16 ± 0.16 eV. These findings are discussed in the context of available theoretical predictions of thermodynamic stability versus the formation of silicon oxide, silicates and silicides and of the band discontinuity problem