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We have used admittance spectroscopy to measure conduction-band and valence-band offsets in Si/Si1−xGex and Si/Si1−x−yGexCy heterostructures grown by solid-source molecular-beam epitaxy. Valence-band offsets measured for Si/Si1−xGex heterojunctions were in excellent agreement with previously reported values. Incorporation of C into Si1−x−yGexCy lowers the valence- and conduction-band-edge energies compared to those in Si1−xGex with the same Ge concentration. Comparison of our measured band offsets with previously reported measurements of energy band gaps in Si1−x−yGexCy and Si1−yCy alloy layers indicate that the band alignment is Type I for the compositions we have studied and that our measured band offsets are in quantitative agreement with these previously reported results.

A four-junction cell design consisting of InGaAs, InGeAsP, GaAs, and GaoslnosP subcells could reach 1xAMO efficiencies of 35.4%. but relies on the integration of nonlattice-matched materials. Wafer bonding and layer transfer processes show promise in the fabrication of InP/Si epitaxial templates for growth of the bottom InGaAs and InGaAsP subcells on a Si support substrate. Subsequent wafer bonding and layer transfer of a thin Ge layer onto the lower subcell stack can serve as an epitaxial template for GaAs and GaoslnosP subcelis. Present results indicate that optically active iliN compound semiconductors can be grown on both Ge/Si and InP/Si heterostructures. Currenk voltage electrical characterization of the interfaces of these structures indicates that both lnP/Si and Ge/Si interfaces have specific resistances lower than O.lncmz for heavily doped wafer bonded interfaces, enabling back surface power extraction from the finished cell structure.

The need for a reference "library" of EELS edges has recently been recognized by several workers, and a partial EELS library has become available for the most common elements at about 3eV resolution. Our work aims at expanding this pool of known spectra to less common elements, and improving the energy resolution to ≤ leV. It is hoped that the resultant library will be useful in several ways: as a source of experimental spectra for testing cross-section calculations and spectra quantitation programs, as a data bank of high-resolution "fingerprint" spectra for elemental identification of unknown samples, and as an educational tool showing the trends and features appropriate to whole classes of elements of similar atomic number.