Raman scattering characterization and electron phonon coupling strength for MeV implanted InP(111)

Abstract

Structural modifications in InP(111) due to 1.5 MeV implantation of Sb have been characterized using first-order and second-order Raman spectroscopy. With both longitudinal optical (LO) and transverse optical (TO) modes allowed for InP(111), we have investigated the evolution of both these modes as a function of fluence. Investigations of both the first and second-order Raman modes indicate the presence of tensile stress in the lattice after implantation, which increases with fluence. Results show a coexistence of nanocrystalline InP regions and amorphous zones in the lattice. Consequently phonon confinement is observed and phonon confinement model (PCM) has been applied here to estimate the coherence length and the size of nanocrystalline zones in InP lattice after implantation. Nanocrystalline zones as small as 35 Å have been observed here. A LO phonon-plasmon coupled mode, due to the charge layer in the vicinity of the surface, has also been observed. This coupled mode becomes sharper and more intense with increasing fluence. For high fluences, crystalline to amorphous phase transition has also been observed. First and second-order LO modes have been utilized to estimate the electron-phonon coupling strengths. The coupling strength is observed to decrease as the nanocrystalline zones, in the implanted lattice, become smaller.