STEM analysis of deformation and B distribution in nanosecond laser ultra-doped Si$_{1-x}$ B$_x$

TL;DR

This study uses STEM analysis to examine how nanosecond laser doping affects the structural properties, defect formation, and boron distribution in highly doped silicon, revealing the relationship between doping levels, defects, and superconductivity.

Contribution

It provides detailed STEM-based insights into the structural and defect evolution in ultra-doped silicon with boron, highlighting the effects of doping concentration on crystalline quality and superconductivity.

Findings

Dislocations and stacking faults appear above 4.3 at.% B doping.

Crystalline quality improves around 8 at.% B doping.

High B concentrations lead to precipitate formation and loss of superconductivity.

Abstract

We report on the structural properties of highly B-doped silicon (> 2 at. %) realised by nanosecond laser doping. We investigate the crystalline quality, deformation and B distribution profile of the doped layer by STEM analysis followed by HAADF contrast studies and GPA, and compare the results to SIMS analyses and Hall measurements. When increasing the active B concentration above 4.3 at.%, the fully strained, perfectly crystalline, Si:B layer starts showing dislocations and stacking faults. These only disappear around 8 at.% when the Si:B layer is well accommodated to the substrate. When increasing B incorporation, we increasingly observe small precipitates, filaments with higher active B concentration and stacking faults. At the highest concentrations studied, large precipitates form, related to the decrease of active B concentration. The structural deformation, defect type and concentration, and active B distribution are connected to the initial increase and subsequent gradual loss of superconductivity.