Shallow defect levels in neutron-irradiated p-type extrinsic silicon

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Abstract
Two new acceptor levels, at 0.027±0.001 eV and 0.039±0.004 eV from the valence band, have been observed by measurements of Hall effect versus temperature in neutron‐irradiated float‐zone‐grown Si : Ga. The presence of these very shallow electronic energy levels was also indicated by photoconductive spectral response measurements at 5 K. The purpose of neutron irradiation was to counterdope residual boron by neutron transmutation for infrared detector applications. These shallow acceptors are observed after anneals at temperatures as high as 625 °C, but annealing at 700–850 °C reduces their concentration below detectable levels. Shallow levels are also observed in neutron‐irradiated Si : Al and Si : In grown by the floating‐zone method. Results indicate that formation of these shallow defects depends upon the presence of column‐III dopant atoms (Ga, In, Al).