Raman_scattering studies of silicon_implanted gallium arsenide: The role of amorphicity

Abstract

A series of Raman_scattering experiments were carried out on GaAsimplanted with Si+ and with SiF+ 3 ions, both before and after annealing, for samples subjected to fluences spanning a wide range. The implantation_induced amorphization of the damage layer was cleanly observed via the evolution, with increasing fluence, of the broad three_band continuum of amorphous GaAs which extends from near zero up to 300 cm_ 1. Annealing recovers the simple line spectrum of crystalline GaAs, but with a changed longitudinal_optical/transverse_optical intensity ratio which indicates a departure from epitaxial regrowth. Three lines observed near 400 cm_ 1 in heavily implanted samples were identified with silicon vibrational local modes. The effect of annealing on these local_mode lines is n o t an intensity increase but is instead a line narrowing which reveals an annealing_induced sharpening of the distribution of local settings sampled by the substitutional silicons. In particular, a line (at 381 cm_ 1) assigned to the Si_at_a_Ga_site donor impurity is clearly seen b e f o r eannealing, even though annealing is needed to transform the highly resistive implantedmaterial into semiconducting n_type GaAs. We propose that the primary role of annealing in the electrical activation of implantedsemiconductors is n o t to shift the impurity atoms into substitutional donor or acceptor sites (they already occupy such sites), but is instead to recover the high carrier mobility of the crystalline form. Healing and activation thus correspond to the same process, the elimination of amorphicity.