Delta -function-shaped Sb-doping profiles in Si(001) obtained using a low-energy accelerated-ion source during molecular-beam epitaxy.

Abstract

Two-dimensional (2D) buried \ensuremath{\delta}-function-shaped Sb-doping profiles have been obtained in Si using a low-energy accelerated Sb-ion source during molecular-beam epitaxy. A combination of secondary-ion mass spectrometry (SIMS), capacitance-voltage (C-V) measurements, and cross-sectional transmission electron microscopy (XTEM) was used to investigate dopant distributions and to determine profile widths. The 2D-sheet Sb-doping concentration ${\mathit{N}}_{\mathrm{Sb}}$, obtained by integrating SIMS \ensuremath{\delta}-doping profiles in samples grown with substrate temperature ${\mathit{T}}_{\mathit{s}}$=620 \ifmmode^\circ\else\textdegree\fi{}C and Sb-ion acceleration potentials ${\mathit{V}}_{\mathrm{Sb}}$=200 and 300 V, was found to vary linearly with the product of the Sb-ion flux and the exposure time (i.e., the ion dose) over the ${\mathit{N}}_{\mathrm{Sb}}$ range from 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ to 2\ifmmode\times\else\texttimes\fi{}${10}^{14}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. The full width at half maximum (FWHM) concentration of \ensuremath{\delta}-doping profiles in Si(001) films was less than the depth resolution of both SIMS and C-V measurements (\ensuremath{\sim}10 and 3 nm, respectively). High-resolution XTEM lattice images show that the FWHM was \ensuremath{\le}2 nm. This is consistent with dopant incorporation simulations, based upon a multisite transition-state dopant incorporation model, which show that accelerated-beam dopant species are trapped in near-surface substitutional sites with atomic mobilities between those of surface and bulk atoms. Dopant surface segregation during growth is strongly suppressed, and the dopant distribution is determined primarily by the straggle in ion trapping distributions. The present results are compared with profile broadening observed in \ensuremath{\delta}-doped layers obtained by solid-phase epitaxy of amorphous Si containing a buried Sb layer.