Far-infrared spectroscopy of folded transverse acoustic phonons in 4H–SiC

The weakest mode of the infrared active folded phonons in 4H–SiC, folded transverse acoustic (FTA) mode, has been experimentally studied. The lifetime of the FTA phonons has been determined. The lifetime is 58 ± 4 ps at room temperature and increases to 140 ± 7 ps when the temperature is decreased to 5 K. These results were obtained by the experimental study of far-infrared transmission of the SiC crystal and its theoretical simulation using an oscillator model for the dielectric function around the phonon resonance. The FTA phonon lifetime was a fitting parameter of the model when analyzing the irregular interference pattern in the transmission spectrum measured with a high resolution (0.2 cm−1). Oscillator strength of the FTA phonon resonance has also been determined. It is equal to (6.0  ± 0.5 ) × 10 − 4 and does not depend on temperature.