High infrared responsivity Indium-doped silicon detector material compensated by neutron transmutation

The use of the neutron transmutation for producing precisely compensated, extrinsic idium-doped, silicon detector material of high infrared responsivity is reported. Highly indium-doped silicon crystals containing (1 to 3) × 10 17 cm -3 indium concentrations and residual acceptors in the low 10 12 cm -3 have been grown by float-zone doping. The high purity obtained by this growth technique enables very low net donor compensation densities to be achieved by neutron irradiation in a reactor. Transmuted phosphorus concentrations ranging from (1 to 20) × 10 12 cm -3 have been investigated and compensation densities, N₃ - N₀, as low as 2 × 10 12 cm -3 have been achieved in irradiated samples after suitable damage annealing. Residual radioactivity due to transmuted indium isotopes approaches negligibly low levels for the neutron fluences required with high purity float-zone Si: In material. Significant improvements in infrared detector performance have been demonstrated with neutron compensated indium-doped silicon. Peak responsivities up to 100 A/W at 50 K and 10 3 -V/cm detector bias have been measured, corresponding to dc photoconductive gains in the 30 to 40 range and mobility-lifetime products > 10 -3 cm 2 /V. Additional studies indicate that the detector responsivity, which is adversely affected by high-temperature CCD fabrication processes, can be restored significantly by phosphorus gettering techniques.