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) × 10¹⁷cm^-3indium concentrations and residual acceptors in the low 10¹²cm^-3have 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) × 10¹²cm^-3have been investigated and compensation densities, , as low as 2 × 10¹²cm^-3have 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 10³-V/cm detector bias have been measured, corresponding to dc photoconductive gains in the 30 to 40 range and mobility-lifetime products > 10^-3cm²/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.