Results from optically detected cyclotron resonance (ODCR) studies of electron effective masses in 4H SiC are reported. ODCR measurements were performed on high-purity n-type 4H SiC epitaxial layers grown by chemical vapor deposition at both X band (9.23 GHz) and Q band (35.05 GHz) microwave frequencies. Electron effective masses in 4H SiC were directly determined as m⊥*=0.42m0 and m∥*=0.29m0. A scattering time in the basal plane τ⊥≊4.3×10−11 s, and hence, the corresponding electron mobility μ⊥≊1.8×105 cm2/V s, was obtained from a fit of the ODCR line shape.

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The structure of nanocrystalline rhenium-silicon composite ReSi x films with 1.4ϽxϽ2.2 has been studied as a function of the time by means of high temperature x-ray diffraction and transmission electron microscopy. Simultaneously, the thermoelectric transport properties were measured during the heat treatment. The nanocrystallization was achieved by annealing of amorphous films deposited onto oxidized Si wafers by magnetron cosputtering. The crystallization process is characterized by a decreasing average crystallite size in the range between 7 and 19 nm. An unknown mechanism limits the grain growth after reaching a maximum size, which decreases with increasing Si content. In the final state the films contain only two phases: the amorphous phase and the nanocrystalline ReSi 1.75 phase. The electrical conductivity and the thermoelectric power of these thin film composites show nonmonotonic dependence on the volume fraction of the nanocrystalline phase and depend on different parameters, which suggests a way to optimize the thermoelectric efficiency.

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