Positron studies of defects in ion-implanted SiC

Abstract

Radiation damage caused by the implantation of 200 keV ${\mathrm{Ge}}^{+}$ ions into 6H-SiC has been studied by monoenergetic positron Doppler broadening and lifetime techniques. Specimens exposed to seven ion fluences ranging from ${10}^{16}$ to ${10}^{19}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$, together with unirradiated samples, were studied. The depth of the damaged crystalline layer was found to range from about 300 to 600 nm and, for ion fluences above 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$, an amorphous layer is seen whose thickness increases to 133 nm at the highest fluence. Positron lifetime measurements, in combination with theoretical calculations, suggest that the main defect produced is the divacancy, but that Si monovacancies are also created. In the amorphous surface layer larger agglomerates consisting of at least four but more probably six vacancies are detected. Trapping rates are evaluated as a function of incident positron energy by applying the positron trapping model to the data. Values for defect concentrations in the damaged layers of about 50 ppm are deduced by invoking plausible assumptions; the problem of extracting defect profiles from the data is discussed. \textcopyright{} 1996 The American Physical Society.