Electrical Studies of Electron-Irradiated Lithium-Containing<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi></mml:math>-Type Silicon

Abstract

Hall-coefficient and resistivity measurements have been used to investigate the crystal growth and irradiation-temperature dependence of the introduction rate and room-temperature annealing of carrier-removal defects in lithium-doped silicon. Initial resistivity of the quartz-crucible silicon was 30 $\ensuremath{\Omega}$ cm and of the float-zone silicon was \ensuremath{\ge}1500 $\ensuremath{\Omega}$ cm. The silicon was doped with lithium to a density of 2\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Irradiations were carried out with 1-MeV electrons at bombardment temperatures ranging from 79 to 280\ifmmode^\circ\else\textdegree\fi{}K. Specimens were annealed to 200\ifmmode^\circ\else\textdegree\fi{}K, thereby separating intrinsic and impurity defects. Introduction rates of carrier-removal defects were exponentially dependent on the reciprocal of temperature for both types of crystal, but the slopes and limiting temperature values differed. The slope of the carrier-removal rate versus reciprocal temperature curve is 0.055 eV in crucible silicon and 0.09 eV in zone-refined silicon. The temperature dependence was not consistent with a simple charge-state-dependent probability of interstitial-vacancy dissociation and impurity-vacancy trapping. Carrier concentrations measured at or near room temperature were increased in zone silicon, but were decreased in crucible silicon by isothermal annealing at room temperature. Crucible-silicon samples annealed to 373\ifmmode^\circ\else\textdegree\fi{}K for 10 min exhibited complete recovery of mobility. Complete recovery of mobility in float-zone-refined silicon took place in an annealing time \ensuremath{\le}17 h at room temperature. The time constant of the annealing kinetics at room temperature is consistent with the observation that the lithium-diffusion constant in oxygen-rich silicon is smaller than that in oxygen-lean silicon. The mechanism of room-temperature annealing is attributed to neutralization of carrier-removal defects by lithium interaction in crucible silicon, and by both lithium interaction and defect dissociation in zone-refined silicon. Results suggest that radiation produces a lithium-oxygen-vacancy complex in quartz-crucible-grown silicon, and a lithium-vacancy complex in float-zone-refined silicon. The LiO-V defect is tightly bound compared to the oxygen-free Li-V defect. Measurements of carrier density as a function of reciprocal temperature located defect-energy levels near ${E}_{c}\ensuremath{-}(0.18 \mathrm{eV})$ and ${E}_{c}\ensuremath{-}(0.13 \mathrm{eV})$, in irradiated-crucible silicon. The former defect level is the $A$ center, and the latter is the reverse annealing center, which is formed at a temperature of 250\ifmmode^\circ\else\textdegree\fi{}K. A defect level located near ${E}_{c}\ensuremath{-}(0.08 \mathrm{eV})$ formed after crucible-silicon samples were annealed at room temperature and lithium interacted with radiation defects.