Capture of free excitons by phosphorus and boron in bilayered silicon crystals

By using a bilayered silicon single crystal, each layer of which contains a different impurity, the capture cross section of free excitons (FE’s) by impurities is accurately determined with a photoluminescence (PL) technique, by taking into account FE diffusion in the crystal. The cross sections for phosphorus in the impurity range ${10}^{10}$–${10}^{12}$ ${\mathrm{mm}}^{\mathrm{-}3}$ and for boron at ${10}^{11}$ ${\mathrm{mm}}^{\mathrm{-}3}$ are (2–6)×${10}^{\mathrm{-}12}$ and (6–7)×${10}^{\mathrm{-}12}$ ${\mathrm{mm}}^2$, respectively, at 4.2 K. With these values together with the Auger rates, the intensity ratios of PL associated with various bound multiexciton complexes can be reasonably explained. In trace-impurity determinations of thin films for indirect-gap semiconductors, using the PL technique, consideration of FE diffusion in the crystal is the key point.