Spreading resistance measurements on doped layers revealed a nonuniform dopant distribution with Sb pile-up at the layer surface, which must be removed by chemomechanical polishing. A BIB detector fabricated from an Sb-doped Ge layer grown on a pure substrate showed a low energy photoconductive onset (~6 meV). A reduction in the donor binding energy due to impurity banding was observed by variable temperature Hall effect measurements. Antimony (~10 16 cm -3) was used as a dopant for the active BIB layer. The graphite distillation and growth components as an additional phosphorus source cannot be ruled out. Lead purification by vacuum distillation and dilution reduced the phosphorus concentration in the layers to ~ 10 14 cm -3 but further reduction was not observed with successive distillation runs. Unintentionally doped Ge layers contained ~10 15 cm -3 phosphorus as determined by Hall effect measurements and Photothermal Ionization Spectroscopy (PTIS).
It was found that the purity more » of the blocking layer was limited by the presence of phosphorus in the lead solvent. Terrace growth was observed, with increasing terrace height for larger misorientation angles. GaAs Blocked-Impurity-Band (BIB) photoconductor detectors have the potential to become the most sensitive, low noise detectors in the far-infrared below 45.5 cm.
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