Temperature Dependence of Raman Scattering in 4H-SiC

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A series of 4H-SiC bulk wafers with different carrier concentrations were studied by Raman scattering in temperature range of 80K to 873K. Different Raman phonon modes of 4H-SiC can be clearly observed. Most Raman peaks of different modes shift to lower frequency with increasing temperature. But abnormal behavior can be observed in the longitudinal optical-plasma coupling mode, which does not decrease in frequency monotonously when temperature increases like other Raman modes. It increases at relatively low temperature and begins to drop after a critical temperature.