Raman scattering evidence of medium-range order in low fluence Se+-implanted GaAs

The effect of growing disorder in the 200 keV Set-implanted GaAs layers has been investigated by Raman scattering for low ion fluences ranging from 1 x 10(12) to 1 x 10(14) cm(-2). We observe a softening and asymmetric broade ning of the symmetry-allowed LO phonon line, and the same effect for the TO peak corresponding to the misoriented, recrystallized parts of the implant ed material. The average diameters of GaAs nanocrystals were determined usi ng a phonon-confinement model. The presence of the background signal attrib uted to a boson peak in the Raman spectra indicates that the medium-range o rder amorphous phase becomes important above the Se+ ion threshold fluence of 8 x 10(12) cm(-2). (C) 2000 Elsevier Science B,V, All rights reserved.