Theoretical and experimental investigation of aluminum-boron codoping of silicon

Abstract

We present a detailed study on aluminum-boron codoping of silicon by alloying from screen-printed aluminum pastes containing boron additives (Al–B pastes). We derive an analytical model for the formation of the Al–B acceptor profiles by quantitatively describing (i) the composition of the Al–B–Si melt and (ii) the incorporation of Al and B acceptor atoms into the recrystallizing Si lattice. We show that measured Al–B dopant profiles can be excellently described by this model, which therefore offers a straightforward method for the comprehensive investigation of alloying from Al–B pastes. The formation of a characteristic kink in the Al–B dopant profile curve can thus be ascribed to the exhaustion of the B additive dissolution during alloying. By intentionally adding elemental B powder to an Al paste, we demonstrate that only a low percentage of the B powder actually dissolves into the melt. We show that this incomplete dissolution of the B additive strongly affects the recombination characteristics of Al–B–p+ regions and, thus, is an important element of alloying from Al–B pastes. This study therefore provides improved understanding of aluminum-boron codoping of silicon. Copyright © 2015 John Wiley & Sons, Ltd.