6 - Ion Implantation Induced Extended Defects in GaAs

Abstract

This chapter focuses on the defects that form upon annealing implanted GaAs and how these defects influence factors such as dopant redistribution and activation. Ion implantation is the accepted method of introducing dopants in GaAs-based microelectronic devices. It is used to form gate, source, and drain regions in high speed field effect transistors. During ion implantation of semiconductors, different amounts of radiation damage can be induced in the substrate. The amount of damage depends on a variety of implant-related factors including the target, implant temperature, ion dose, ion mass, ion energy, and dose rate. The defects can be classified using the same scheme developed for implantation-related defects in silicon. Type I defects are typically extrinsic dislocation loops or voids. For species which diffuse interstitially, dislocation loops may influence the diffusivity, possibly by trapping extra interstitials created by the implantation process. Type II dislocations are very unstable in GaAs. Type III defects are believed to form because of local deviations in the stoichiometry and the low diffusivity of Ga and As at the regrowth temperatures. Type IV defects form upon annealing a buried amorphous layer. These defects form at the position where the two advancing amorphous or crystalline interfaces meet. Finally, type V defects consist of either precipitates, dislocation loops, or both.