Donor-bound-exciton strain microscopy in silicon devices

Abstract

We explore the effects of stress on silicon donor bound exciton ($\mathrm{D^0X}$) transitions in bulk silicon and in microfabricated silicon devices. We first study $\mathrm{D^0X}$ transitions in an isotopically purified silicon-28 bulk doped sample under controlled uniaxial stress, confirming the validity of existing models in the low strain ($\lesssim 10^{-5}$) regime. We then demonstrate the localised photoconductive detection of a few thousand donors illuminated by a 1078 nm resonant laser with $4~\mathrm{\mu m}$ spot focused on a microfabricated device consisting of an implanted phosphorus layer between a pair of metallic contacts. We observe local variations in the strained exciton peak splitting from $10~\mathrm{\mu eV}$ to $200~\mathrm{\mu eV}$, and obtain scanning microscopy stress maps in good agreement with finite-element-model thermal stress simulations. Our results suggest a potential use of donor bound excitons for in-situ stress sensing, and demonstrate pathways for the miniaturisation of $\mathrm{D^0X}$ photoconductive detection.