Pr4f occupancy and VB/CB band offsets of Pr 2 O 3 at the interface to Si(001) and SiC(0001) surfaces
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Pr4f occupancy and VB/CB band offsets of Pr2O3 at the interface to Si(001) and SiC(0001) surfaces Dieter Schmeißer and H.J. Muessig Angewandte Physik - Sensorik, BTU Cottbus, Postfach 10 13 44, 03044 Cottbus, Germany ihp, Im Technologiepark 25, 15236 Frankfurt/Oder, Germany. Abstract Resonant photoelectron spectroscopy (PES) at the Pr4d and O1s absorption edges is used to study the electronic properties at the interface of epitaxial grown Pr2O3 on Si(001). In the electronic structure of bulk Pr2O3 the valence band (VB) states are predominantly of Pr6s and O2p atomic parentage. The contribution of Pr4f states are identified from the strong increase the VB features at the Pr4d resonances. The data at the O1s edge are caused by Raman scattering and resonant Auger decay and reflect the existence of CT complexes. They are the consequence of mixed valency caused by ligand-to-Pr4f charge transfer states. The decrease of their intensity is attributed to an increase in covalent bandwidth between the Ligand (O2p, Si3p) and Pr4f states. The CT complexes originally localized now become broadened and form gap states which fill the gap towards a metallic density of states. The metallic phase may be hindered upon alloying with SiO2 or other oxides Introduction The current roadblock in the semiconductor technology road map (and in Moore’s law) is the shrinking width of the SiO2 layer that insulates the gate from the channel of a transistor. The latest devices by Intel and others approach a few atomic layers and gives rise to unsupportable leakage currents via tunneling. This has triggered an intensive search for gate insulators with a high dielectric constant, where the layer can be made thicker without compromising the capacitance /1, 2/. We present a study of the fundamental interface properties of such a material (praseodymium oxide) at the Si(100) interface and we compare these results to Pr2O3 films grown on SiC(0001) surfaces. In this contribution we focus on the Pr4f occupancy in the occupied VB states and in the empty CB states. We obtain such kind of chemical information by comparing the resonant PES around the O1s threshold for CeO2, Ce2O3, and Pr2O3 in the bulk oxidic phase which represents a series with increasing the number of available f-electron in the particular system. We realize, that upon increasing the number of 4f electrons also the covalent contribution increases. This is the main reason why in the Pr-O-Si system we deduce that the localized nature of the 4f electrons is fully vanished and we find covalent broadened 4f states as gap states with a continuous density of states (DOS). Experimental Experiments are performed at the U49/2 beam line at BESSY equipped with a PEEM used to record the XAS data and a hemispherical electron energy analyzer for the photoelectron spectra /3/. Pr is evaporated from an e-beam evaporator with the Si(001) surface kept at 600°C after removing the native SiO2 layer by flashing. The bulk phases of CeO2 and Pr2O3 are prepared from concentrated nitrate solutions deposited on
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