The angular- and crystal-momentum transfer through electron–phonon coupling in silicon and silicon-carbide: similarities and differences

Electron–phonon scattering has been studied for silicon carbide (6H-SiC) with resonant inelastic x-ray scattering at the silicon 2p edge. The observed electron–phonon scattering yields a crystal momentum transfer rate per average phonon in 6H-SiC of 1.8 fs−1 while it is 0.2 fs−1 in crystalline silicon. The angular momentum transfer rate per average phonon for 6H-SiC is 0.1 fs−1, which is much higher than 0.0035 fs−1 obtained for crystalline silicon in a previous study. The higher electron–phonon scattering rates in 6H-SiC are a result of the larger electron localization at the silicon atoms in 6H-SiC as compared to crystalline silicon. While delocalized valence electrons can screen effectively (part of) the electron–phonon interaction, this effect is suppressed for 6H-SiC in comparison to crystalline silicon. Smaller contributions to the difference in electron–phonon scattering rates between 6H-SiC and silicon arise from the lower atomic mass of carbon versus silicon and the difference in local symmetry.

Source:IOPscience

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Characterization of tungsten–nickel simultaneous Ohmic contacts to p- and n-type 4H-SiC

Ohmic contacts to p- and n-type 4H-SiC using refractory alloyed W:Ni thin films were investigated. Transfer length measurement test structures to p-type 4H-SiC (NA = 3 × 1020 cm−3) revealed Ohmic contacts with specific contact resistances, ρc, of ~10−5 Ω cm2 after 0.5 h annealing in argon at temperatures of 1000 °C, 1100 °C, 1150 °C, and 1200 °C. Contacts fabricated on n-type 4H-SiC (ND = 2 × 1019 cm−3) by similar methods were shown to have similar specific contact resistance values after annealing, demonstrating simultaneous Ohmic contact formation for W:Ni alloys on 4H-SiC. The lowest ρc values were (7.3 ± 0.9) × 10−6 Ω cm2 for p-SiC and (6.8 ± 3.1) × 10−6 Ω cm2 for n-SiC after annealing at 1150 °C. X-ray diffraction shows a cubic tungsten–nickel–carbide phase in the Ohmic contacts after annealing as well as WC after higher temperatures. Auger electron spectroscopy depth profiles support the presence of metal carbide regions above a nickel and silicon-rich region near the interface. X-ray energy dispersive spectroscopy mapping showed tungsten-rich and nickel-rich regions after annealing at 1100 °C and above. W:Ni alloys show promise as simultaneous Ohmic contacts to p- and n-SiC, offering low and comparable ρc values along with the formation of WxNiyC.

Source:IOPscience

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Silicon carbide of Ni/6H-SiC and Ti/4H-SiC type Schottky diode current-voltage characteristics modelling

On the base of the physical analytical models based on Poisson's equation, drift–diffusion and continuity equations the forward current–voltage characteristics of 6H-SiC and 4H-SiC type Schottky diode with Ni and Ti Schottky contact have been simulated. It is shown on the base of analysis of current–voltage characteristics in terms of classical thermionic emission theory it is shown that the proposed simulation model of Schottky diode corresponds to the almost "ideal" diode with ideality factor n equals 1.1. Because of this it is determined that the effective Schottky barrier height B equals 1.57 eV and 1.17 eV for Ni/6H and Ti/4H silicon carbide Schottky diode type, respectively.

Source:IOPscience

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