Electron and Phonon Coupling Dynamics in Low-Gap Semiconductor: Quantum versus Classical Scale

Abstract

We have studied the characteristics of longitudinal-optical-phonon-plasmon coupled (LOPC) mode by using the ultrashort pulsed laser with 45 THz bandwidth as a function of thickness in InAs epilayers, ranging from 10 to 900 nm. We have observed the LOPC modes split into the upper (L+ mode) and the lower (L- mode) branches only in the classical scale, but the longitudinal-optical (LO) phonon peak was persistently observed. The shorter decay time of the plasmon-like L+ modes rather than the phonon-like L- modes should be associated with carrier-carrier scattering which is further considered with diffusion properties in the low-gap semiconductors. This result leads to that the absence of the LOPC modes in a scale less than exciton Bohr radius manifests the role of electron diffusion rather than the carrier screening via drift motion in surface depletion region.