Vacancy-related deep levels inn-typeSi1−xGexstrained layers

Abstract

Deep-level transient spectroscopy (DLTS) studies of 2-MeV proton-induced defect electronic levels in strained epitaxial ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x},$ $0<~x<~0.13,$ layers have been performed. It is found that the irradiation results in the formation of a dominant peak in the DLTS spectra for all compositions. Isochronal 20-min annealing studies of the observed deep level have revealed that the peak anneals out at 100--200 \ifmmode^\circ\else\textdegree\fi{}C. This peak is identified as the vacancy-phosphorous (VP) pair. The compositional dependence of the activation enthalpy of the VP pair is nonlinear, with a sharp increase for $x=0.04$ and little variation for higher Ge concentrations. After annealing of the VP pair, the dominating defect level is assigned to the single acceptor state of the divacancy $[{V}_{2}(\ensuremath{-}/0)].$ The double-acceptor state $[{V}_{2}(=/\ensuremath{-})]$ is observed to be strongly suppressed in the strained ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ layers. The compositional dependence of the activation enthalpy of ${V}_{2}(\ensuremath{-}/0)$ is relatively weak, with a small decrease in the activation enthalpy. It is found that formation of ${V}_{2}$ in the strained ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ layers is enhanced with respect to that in Si. This is associated with an increased concentration of vacancies in the strained layer, acting as a sink for vacancies migrating in the substrate.