Thermal Dephasing of Localized Vibrations and Quasi-Elastic Scattering in Heavily Doped Silicon: Raman Spectroscopic Evidence

Raman signature corresponding to quasi elastic scattering (QES) has been discovered where the local vibrational mode (LVM) B¹¹, present in heavily doped p-type (boron doped) silicon (Si), participate in Raman scattering. The LVM manifests itself as an asymmetric Raman line-shape due to Fano resonance which gets weakened on increasing temperature as revealed through temperature dependent Raman spectroscopy and Raman thermal mapping. The temperature dependent Raman experiment, combined with the modified Balkanski model for the LVM, reveals that the increase in Raman line width (fwhm) with temperature does not originate from the direct anharmonic phonon decay rather QES is taking place. In particular, the presence of Fano coupling between the local vibrational mode B¹¹ and the electronic continuum serves as a significant probe for exploring the quantum behavior of such material. The observed reduction in Fano coupling strength, duly quantified by Fano parameter, accompanied by an increase in fwhm of the Raman line shape with rising temperature, has been analyzed to confirm the presence of QES. Evidence of the phonons' dephasing (loss of coherence) process with temperature in LVM has been identified. This dephasing arises from the suppression of quantum interference between the discrete localized mode B¹¹ and the electronic continuum. Overall the findings present an improved insight about the physical processes taking place at the microscopic level in a heavily doped semiconductor.