[22a-C102-1~8] 22.1 Joint Session M "Phonon Engineering"

△ [22a-C102-5] Femtosecond spectroscopy of coherent acoustic phonons in silicon thin films with different crystallinities

〇Yui Miyanaga¹, Ya Zhang¹ (1.TUAT.)

Keywords:Coherent acoustic phonons, semiconductor

Acoustic phonons in the GHz and terahertz frequency bands are known to be responsible for the heat transport in solids. Observation of the phonon propagations is therefore very crucial for the study of the heat transport process. In this research, we aim at investigating the phonon propagation process in thin silicon films with different crystallinity conditions. We fabricate 800nm-thick silicon membranes. A 30nm aluminum layer is deposited on the membrane as a photo-phonon transducer. We perform femtosecond(fs) laser pump and probe measurement for the silicon membrane sample. A 400nm fs laser pulse is used as a pump light to excite acoustic phonons in the Al layer through the photothermal effect. The excited phonon pulse changes the refractive index of the Al layer, which is probed by an 800nm probe light pulse as the reflectivity change of the Al layer. Two echoes of the excited phonons are observed by tuning the time delay between the pump and the probe light. By comparing the two echoes, we find that there is significant decay in the phonon amplitude and a change in the pulse shape during the travelling in the membrane, which may contain useful information on the phonon transmission properties of silicon material.