Raman scattering from phonon-plasmon modes in gallium arsenide implanted by silicon ions

Abstract

Raman spectra (RS) of (100) GaAs implanted with 140 keV Si + ions, both before and after annealing, were obtained at room temperature, in x(yz)x backscattering geometry, using the 514.5 nm line of Ar laser. The implantation-induced amorphous bands and LO-line shape changes were observed with increasing fluences from 10 13 to 5 X 10 14 cm -2 . We explained the modifications of the spectra via disorder-induced selection rule breakdown and estimated nanocrystallite size for different fluences according to the model of reduction of the spatial correlation length. For annealing studies implanted samples were capped with Si 3 N 4 layer and annealed at 900 C for 20 min in hydrogen. After annealing, the amorphous bands have disappeared, and the new spectral features were observed. We examples the evolution of the spectra by the dopant activation, resulting in RS by phonon- plasmon coupled modes and RS by LO phonon, originating from the surface-depletion layer. We interpreted shifts of the coupled modes and LO intensity change as evidence of the carrier concentration variation with fluences. Experimental result were described by the Lindhard-Mermin dielectric function including the non-parabolicity of the conduction band, evaluated for the case, when Drude approximation is not available. From Raman line-shape analysis we have obtained that the value of carrier concentration were 10 18 cm -3 for ion fluences 10 13 -5 X 10 14 cm -2 .