Interface‐Specific Excitation of Coherent Phonons at the Buried GaP/Si(001) Heterointerface

Abstract Ultrafast charge‐carrier and phonon dynamics at the buried heterointerface of GaP/Si(001) are investigated by means of two‐color pump‐probe reflectivity measurements. The carrier‐induced reflectivity signal exhibits a resonant enhancement at a pump‐photon energy of 1.4 eV, which is assigned to an optical transition at the interface. In addition, the transient reflectivity is modulated by a coherent oscillation at 2 THz, whose amplitude also becomes maximum at 1.4 eV. The observed resonant behavior of the oscillation, in combination with the characteristic wavelength‐dependencies of its frequency and its initial phase, strongly indicates that the 2‐THz mode is a difference‐combination mode between a GaP‐like and a Si‐like phonon at the heterointerface and that the corresponding second‐order Raman scattering process can be enhanced by a double resonance involving the interfacial electronic states.