An intensive search for alternatives to SiO2 as gate dielectric with higher dielectric constant, å , started in recent years. Crystalline instead of amorphous growth can potentially further reduce the concentration of defects below the level of amorphous or policrystalline material. Therefore, we investigated the low temperature growth conditions of mixed Ba0.7Sr0.3O layers on Si(100), for which, as we show, their miscibility can directly be used to obtain a perfect lattice match. The investigations were carried out by a combination of LEED, x-ray photoemission and electron energy loss spectroscopy.
Oxide films were created by evaporation of the Sr and Ba metals in oxygen atmosphere to the Si(100) sample at room temperature after preadsorption of 1ML of either metal. Quantitative LEED analyses showed that the films are closed and smooth with an rms roughness of about 1 layer at a thickness of 10 layers. In XPS the starting metal interface layer grown at 650° C leaves the Si2p unchanged and no evidence for the formation of silicide was found under all conditions tested. No SiO2 is formed either. The formation of the oxide layer is characterized by two oxygen species that are strictly localized at the interface: a mono-coordinated SiO that saturates at half a monolayer, and a mixed Sr-O-Si species with a saturation concentration of 1 ML. A band gap of 4.3 eV was found with EELS, independent of layer thickness and starting at 2 ML. Band offsets, determined by XPS, are 2.2 and 1.0 eV for valence and conduction bands, respectively, starting with an Sr interlayer. A more symmetric offset was obtained for Ba as starting layer. Electrical measurements after capping the oxide with gold films revealed an å around 25, low concentrations of defects at the interface and low leakage currents even for oxide thicknesses below 5 nm.
By use of doubly doubly stepped Si(100)-[011]4°, we successfully show that these oxide films can be prestructured by the substrate as template. The oxide follows perfectly this stepped surface, demonstrating possibilities for further structuring of insulator layers using the substrate as template. First results on color center formation both on amorphous and crystalline oxides will further be presented. |