RAMAN-SCATTERING PROBE OF ION-IMPLANTED AND PULSE LASER ANNEALED GAAS

We report Raman scattering studies of phosphorus-ion-implanted and sub sequently pulse laser annealed (PLA) GaAs. The threshold value of impl antation fluence fur the disappearance of one-phonon modes in the Rama n spectrum of ion-implanted GaAs sample is found to be greater than th at for the two-phonon modes by an order of magnitude. The phonon corre lation length decreases with increasing disorder. The lattice reconstr uction process during PLA creates microcrystallites for incomplete ann ealing, whose sizes can be given by the phonon correlation lengths, an d are found to increase with the annealing power density. The intensit y ratio of the Raman spectra corresponding to the allowed longitudinal -optical (LO)-phonon mode to the forbidden transverse-optical (TO)-pho non mode, I-LO/I-TO, is used as a quantitative measure of crystallinit y in the implantation and PLA processes. The threshold annealing power density is estimated to be 20 MW/cm(2) for 70 keV phosphorus-ion-impl anted GaAs at a fluence of 5x10(15) ions/cm(2). The localized vibratio nal mode of phosphorus is observed in PLA samples for fluences above 1 x 10(15) ions/cm(2). (C) 1996 American Institute of Physics.