The Retention of Bi Ions Implanted in GaAs

Abstract

Ion implantation of solids including semiconductors, is rapidly becoming an established technique for changing the composition of solids in an apparently controlled manner, to depths of the order of the ion penetration range. There are definite limits to composition change, which can be effected however, and these limits will be determined by processes such as precipitation and phase segregation of the implant, diffusion of the implant deeper into the solid and out of the solid and sputtering of the solid surface with concomitant removal of the dopant. Examples of the former processes are the precipitation of Au in Si and the diffusion of Cd in Si at elevated temperatures but the role of sputtering in determining dopant concentration in semiconductors seems to have been appreciated but ignored. A cogent reason for this lack of investigation so far, is that in most implantation schedules of contemporary interest, the ion dose is so low (< 10¹⁵/cm²), that the depth of crystal eroded by sputtering is only of the order of tens of atom layers, compared to the depth of ion penetration (the doping depth) which is usually at least an order of magnitude larger than this.