Analysis of superconducting silicon epilayers by atom probe tomography: composition and evaporation field

Abstract

Three dimensional distributions of boron atoms incorporated into crystalline silicon (3-9 at.% of boron) well above the solubility limit are measured by atom probe tomography (APT). Samples have been prepared either by gas immersion laser doping (GILD) or by implantation followed by laser annealing (Pulsed Laser Induced Epitaxy: PLIE). GILD and PLIE silicon samples show superconducting properties at low temperatures due to the achieved their high doping level achieved. In both cases, boron atoms are found to be randomly distributed throughout the silicon as revealed by statistical distribution analysis. No clusters or precipitates are detected, which may be related to the high recrystallization rate of the Si:B alloy. A sharp 2D interface between the doped silicon region and the undoped substrate is also observed, characterizing a Si:B/Si epitaxy. Finally, the variation of the evaporation field is investigated by considering either the silicon charge state ratio or the variation of the total applied voltage during the analysis of the Si:B layer and silicon.