SHALLOW DEFECT LEVELS IN NEUTRON-IRRADIATED P-TYPE EXTRINSIC SILICON

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).