Recombination Centers in Gamma-Irradiated Silicon

Abstract

The minority carrier lifetime in gamma-irradiated silicon crystals was studied. The doping impurity was phosphorus, arsenic, or boron, and the crystals were either float-zoned or pulled from the melt. The silicon E center was found to be the dominant recombination center in float-zoned, n-type crystals after irradiation. The capture cross section of the center for holes was measured to be 1.1×10−13 cm2 in phosphorus-doped silicon. The activation energy for annealing of an E center has been reported to be 0.94 eV, and the corresponding activation energy for the annealing in arsenic-doped crystals was found to be 1.5 eV. After annealing at 160°C, where the E center is known to anneal, the existence of some other energy level at about 0.4 eV below the conduction band was detected. In crystals other than float-zoned n-type, the A center governed the recombination. The cross section of this center was found to be 1.5×10−14 cm2 for holes and 2×10−16 cm2 for electrons. The introduction rate of the A center was found to be the same for a variety of samples. The value was 1.3×10−3 defects/cm3 per photons/cm2.