[Low-temperature-dependent characteristics of Raman scattering in N-type 4H-SiC]

In the present paper, Raman scattering techniques for N-type 4H-SiC single crystal material were performed at the temperatures ranging from 30 to 300 K. These measurements revealed that the Raman phonon modes have a redshift and the linewidth gradually broadens with temperature increasing. Based on the experimental results, the reason for the redshift and broadening is discussed. With the temperature increasing, the lattice thermal vibration restoring force decreases with the lattice thermal vibration increasing, and the interaction between the atom and unit cell is weakened, resulting in the redshift of the acoustic phonon modes and optical phonon modes. The mean number of phonons increase with the temperature increasing, which leads to an increase in scattering probability, in result of decreasing the phonon lifetime. The linewidth and phonon lifetime is inversely proportional, so the linewidth gradually broadens with temperature increasing. Phonon mode intensity with increasing temperature showed different laws that the intensity of E2 (LA), E2 (TA), E1 (TA) and A1 (LA) phonon mode monotonously increases as the temperature increases, while the intensity of E2 (TO), E1 (TO) and A1 (LO) phonon mode decreases after 138 K. The reason is that the high-energy phonons split into multiple lower energy phonons.