Shallow Defect Levels in Neutron Irradiated Extrinsic P-Type Silicon
Two shallow levels, at 0.027 eV and 0.039 eV from the valence band, measured by Hall effect vs. temperature, have been observed in neutron irradiated, float zone (FZ) grown Si: Ga. The neutron irradiation was for the purpose of counter-doping residual boron by producing phosphorus by neutron transmutation 3 0Si (n, γ)3 1Si → 3 1P + β- to allow the Si: Ga to be used as extrinsic Si detector material. These defect levels are observable after 575° to 625°C anneals. Annealing at 700°C - 850°C removes observable radiation defects. Analysis of the Hall effect vs. temperature data indicates that the two levels are acceptors with concentrations in the range 1014- 1015/cm3, in excess of the B concentration of ≴ 2 x 1013/cm3 measured before irradiation. A proportionality between defect concentration and Ga concentration is observed. The shallow levels appear also in photoconductivity spectral response measurements at 5K. Observations of shallow levels in FZ-grown Si: Al and Si: In will also be discussed.
KeywordsHall Effect Shallow Level Float Zone Shallow Defect Neutron Transmutation Doping
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