Activation of group III combinations in silicon and modifications introduced by nitrogen

Abstract

A series of experiments were initiated after finding that a supersteep retrograde channel of an n-channel silicon-based field effect transistor would not have an acceptable threshold voltage if created with indium and sufficient nitrogen (4×1014/cm2) present to retard gate oxide growth. A set of combinations of indium, boron, and nitrogen and a set of combinations of gallium, boron, and nitrogen were examined. It was found that nitrogen caused minimal reduction in the electrical activity of boron, greater reduction with indium, and greatest reduction with indium plus boron. Similar results, though of lesser magnitude, were observed with the gallium set. The chemical profiles of the various dopants in combination with each other gave no indication of the active carrier profile associated with each combination. Theoretical criteria were formulated to attempt to correlate atomic level configurations with electrical activity. Ab initio pseudopotential calculations using the Vienna Ab initio Simulation Package followed; the theoretical criteria correlated very well with the observed electrical activity of the various combinations and, to a lesser degree, with the ordering of nitrogen retention as a function of those combinations. The calculations appear to demonstrate the presence of long range interactions.