Yevgen Burkov

PEEM and μ-NEXAFS of CuInS2-surfaces

Abstract Polycrystalline CuInS 2 samples are an ideal system for photoemission electron microscope studies. The polycrystalline grains have a diameter of approximately 5 μm and the system is expected to be highly inhomogeneous because of the existence of many sub-phases. We used a recently established procedure to reproducibly obtain stoichiometric CuInS 2 -surfaces and follow the changes in the morphology, the elemental inhomogeneous distribution, and the development of the electronic structure upon its preparation. We find that the individual grains trend to coagulate, the surface composition becomes more homogeneous, and identify characteristic features of the unoccupied DOS.

Al-oxynitride interfacial layer investigations for PrXOY on SiC and Si

We investigate the dielectric properties of Praseodymium based oxides PrXOY by preparing MIS (metal insulator semiconductor) structures consisting of PrXOY as a high-k insulating layer and silicon (Si) or silicon carbide (SiC) as semiconductor substrates. The use of a buffer layer between PrXOY and the semiconductor is necessary as we found deleterious reactions between these materials such as silicate and graphite formation. Possessing a higher permittivity value (er) than silicon dioxide (SiO2) and good lattice matching in conjunction with similar thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. In our spectroscopic investigations we found a decrease or indeed prevention of silicon diffusion into the oxide and an increased Pr2O3 fraction after deposition. In electrical characterizations of PrXOY/AlON stacks we found considerable improvements in the leakage current by several orders on both substrates, especially on silicon where we obtain values down to 10−7A/cm2 at a CET (capacitance equivalent thickness) of 4nm. We observed interface state densities in the range of 5 × 1011-1 × 1012/eVcm2 and 1-5 × 1012/eVcm2 on Si and SiC, respectively.

Al-Oxynitride Buffer Layer Facilities for PrO X /SiC Interfaces

We investigate the dielectric properties of Praseodymium based oxides and silicates by preparing MIS structures consisting of a metal layer (M), PrO X (praseodymium oxide) as a high-k insulating layer (I), and silicon (Si) or silicon carbide (SiC) as semiconductor substrates (S). The use of a buffer layer between PrO X and SiC is necessary as we found destructive interactions like silicate and graphite formation between these materials. Based on a higher permittivity value than SiO 2 and a good lattice matching in conjunction with nearly the same thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. We report on results achieved by Synchrotron Radiation Photoemission Spectroscopy (SRPES) and by electrical measurements. In our spectroscopic investigations we found a stable AlON/3C-SiC interface as well as no elemental carbon and silicate contributions in the core levels after thin PrO X deposition and annealing up to 900°C. In electrical characterizations of PrO X /AlON stacks on silicon we already found a strong improvement in the leakage current down to values of 10 -7 A/cm 2 at an CET of 4nm. We observed an interface state density in the range of 5x10 11 -1x10 12 /eVcm 2 and 1-5x10 12 /eVcm 2 on Si and SiC, respectively.