Diffusion and electrical activity of copper in Si 1− x− yGe xC y alloys

Abstract

We investigate copper diffusion in Si-rich Si 1− x− y Ge x C y ( x<20%) and Ge-rich ( x=93%) Si 1− x Ge x layers. The profiles of the different constituents (Si, Ge, Cu, C, B) were determined using secondary ion mass spectroscopy (SIMS). Carrier profiles were studied by electrical characterizations of Schottky diodes. The structures were prepared by copper deposition on SiGeC alloys at room temperature. The increase of the Ge-content from 0% to 93% results in a decrease of the Cu diffusion depth determined by SIMS. C-incorporation also leads to a reduction of Cu-diffusion. The effect of boron seems to be more important, and Cu-diffusion is well retarded in p-type samples. The electrical activity of Cu in IV–IV alloys depends on the Ge-content. For Si-rich p-type SiGe alloy, we observed a passivation of the boron acceptors attributed to the formation of Cu–B pairs, which also explains the reduction of Cu diffusion. For p-type Ge-rich samples, the acceptor concentration can reach very high values (larger than the boron concentration), and becomes temperature dependent. These results show that boron passivation is no longer the most important effect of Cu diffusion. We suggest that the presence of Cu in Ge-rich alloys produces an acceptor-like trap.