研究目的
Investigating the Raman scattering properties of very thin layers of gallium sulfide (GaS) as a function of sample thickness and temperature.
研究成果
Samples of different thickness from a single layer to a bulk GaS crystal were obtained as a result of micromechanical exfoliation. The thicknesses of these samples were determined from AFM measurements. The correlation between the position of the A1g Raman peaks and the thickness of the sample was found. An empirical formula has been proposed that can be used to determine the thickness of the GaS thin films based on Raman measurement. The first-order temperature coefficients of Raman frequency shifts were determined for different sample thickness. The linear softening of the modes with increasing temperature was observed. Optical A1g phonons in studied layers of GaS exhibit temperature dependence of their Raman shift typical for 3-phonon coupling and thermal expansion.
研究不足
The observed broadening of Raman peaks is a direct result of shortening the phonon lifetime in very thin samples. This effect can influence the thermal and electrical properties of very thin GaS layers. It should also take into account, that the very low intensity of the Raman A1g peaks in the case of very thin GaS layers and the proximity of the 2TA mode coming from the Si substrate, affect the error in determining the FWHM of both modes.
