Infrared Studies of Defect Production in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi></mml:math>-Type Si: Irradiation-Temperature Dependence

Abstract

Infrared absorption measurements of electron-irradiated oxygen-doped $n$-type silicon are presented. The silicon samples were electron irradiated at carefully controlled irradiation temperatures between 75\ifmmode^\circ\else\textdegree\fi{}K and room temperature. Since the free Si vacancy, and presumably also the free Si interstitial, are mobile at these temperatures, intensity measurements of the vacancy-oxygen center, as well as of newly observed infrared absorption bands, provide a monitor of the intrinsic defect production. For irradiation temperatures below 100\ifmmode^\circ\else\textdegree\fi{}K, semilog plots of the intensities of the absorption bands for identical samples versus the reciprocals of their irradiation temperatures yield straight lines having the form $\ensuremath{\alpha}=\mathrm{const} {e}^{\frac{\ensuremath{-}\ensuremath{\Delta}E}{\mathrm{kT}}}$. On the basis of the slopes and intensities of these lines, the absorption bands can be divided into two groups. The more intense group, which includes the 836-${\mathrm{cm}}^{\ensuremath{-}1}$ ($A$-center) band and bands at 922, 932, and 865 ${\mathrm{cm}}^{\ensuremath{-}1}$, has a common energy $\ensuremath{\Delta}E=0.05\ifmmode\pm\else\textpm\fi{}0.005$ eV. Less intense bands at 936, 945, and 956 ${\mathrm{cm}}^{\ensuremath{-}1}$ are found to have a common energy $\ensuremath{\Delta}{E}^{\ensuremath{'}}=0.10\ifmmode\pm\else\textpm\fi{}0.02$ eV. These results are interpreted on the basis of a metastable interstitial-vacancy pair model in which the irradiation-temperature dependence of the formation of the defect-impurity complexes results from the temperature dependence of the production of intrinsic defects. On the basis of this model, the difference in the barriers to liberation and recombination of the metastable pair is 0.05 eV for $n$-type Si. The more intense infrared bands are concluded to be associated with complexes composed of a single vacancy or a single interstitial trapped at an oxygen impurity atom or group of atoms. Since the energies $\ensuremath{\Delta}{E}^{\ensuremath{'}}$ of the weaker infrared absorption bands are approximately twice those for the strong infrared bands, it is suggested that the weaker bands are associated with complexes composed of two intrinsic defects trapped at an oxygen impurity center.