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 B % at.) 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 temperature thanks to the achieved high doping level. In both cases, boron atoms are found to be randomly distributed within the silicon as revealed by statistical distribution analysis. No cluster or precipitate are detected, which can be related to the high speed of recrystallization 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 in both materials by considering either the silicon charge states ratio or the variation of the total voltage applied during the analysis of the Si:B layer.