SPIN 1 CENTERS IN NEUTRON IRRADIATED SILICON
Electron paramagnetic resonance of radioinduced defects in neutron irradiated silicon crystals was studied. Measurements were made as a function of annealing on samples which attained intrinsic resistivity after fast neutron bombardment in a reactor. The measurements were made at temperatures of 500, 77, and 4.2 deg K, with superheterodyne spectrometers operating at 24 and 9.4 kmc/s. Through analysis of the anisotropy of the resonance spectra, isochronal annealing experiments, and field dependence of the spectra at 24 and 9.4 kmc/s, four spin-1 centers were isolated. The g-tensors and the magnitude of the zero field splitting terms were compatible with systems having a pair of electrons primarily localized in two (111) dangling bond orbitals separated from each other along a (110) direction by a distance of the order of a lattice spacing. The observed resonance arose from the triplet levels produced by a weak exchange interaction. From the low temperature measurements, an upper limit of the triplet-singlet separation was estimated to be 50 cm/sup -1/. In view of the distinct symmetry of the spectra and the very small production rate of approximates 0.05 centers per neutron collision, they probably repreaent a rather small class of relatively simple, well-defined defects. Each center was observed in comparable concentrations in samples from at least two independent sources, and it appeared unlikely that any impurity other than oxygen was involved. The entire resonance spectrum at 300 and 77 deg K of intrinsic silicon samples after neutron irradiation near approximates 50 deg C was accounted for by centers (II III) and IX. In crucible-grown samples annealed to higher temperatures after irradiation, the centers reported accounted for the most prominent parts of the spectra; however, at each stage of annealing, perhaps one or two additional centers were present and gave as yet unaccounted lines having amplitudes of up to 30% of the main lines. Some of these lines were very broad and represented substantial concentrations. Vacuum floating zone and crucible grown samples gave substantially identical spectra up to the 250 deg C annealing stage, showing centers (II, III), IX, and N to be independent of oxygen. At higher annealing temperatures, the rapid and complex sequence of growth and decay of the centers which were observed only in crucible grown samples suggested a role for oxygen, probably as a constituent, and a connection with the coagulation of oxygen in the formation of these centers. Analysis of the hyperfine interaction tensor of center (II, III) showed that a pair of orbitals of 18% 3s and 82% 3p character, each localized at lattice sites and aligned along the same (111) direction account for 56% of the wave function of each electron. (Dissertation Abstr.)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-037286
- OSTI ID:
- 4630882
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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