Sb surface segregation during epitaxial growth of SiGe heterostructures: The effects of Ge composition and biaxial stress

Abstract

Antimony is the most widely used n-type dopant for Si molecular-beam epitaxy (MBE). However, because of surface segregation during growth, the control of doping profiles remains difficult. The case of ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ heterostructures is complicated by the existence of stresses, which may affect both the thermodynamics and kinetics of segregation. In this study, we analyze the segregation of Sb resulting from the MBE growth of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}/\mathrm{Si}(100)$ heterostructures using secondary ion mass spectrometry as a function of (i) growth temperature $(200\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}l~T\ifmmode^\circ\else\textdegree\fi{}l~550\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ (ii) germanium content $(0l~xl~0.2),$ and (iii) stresses (compressively strained and relaxed layers). We show that Sb segregation: (i) increases with temperature, (ii) increases with Ge content in biaxially compressed layers, (iii) decreases with Ge content in relaxed layers. The temperature variation indicates that Sb surface segregation during growth is kinetically controlled. The contrasting behaviors observed as a function of Ge content in stressed and relaxed layers can thus be explained by a decrease of the segregation enthalpy induced by Ge addition and an increase of near-surface diffusion in stressed layers.