Liquid phase epitaxial growth and characterization of germanium far infrared blocked impurity band detectors

Germanium Blocked Impurity Band (BIB) detectors require a high purity blocking layer (<1013 cm−3) approximately 1 μm thick grown on a heavily doped active layer (∼10 16 cm−3 approximately 20 μm thick. Epilayers were grown using liquid phase epitaxy (LPE) of germanium out of lead solution.; The effects of the crystallographic orientation of the germanium substrate on LPE growth modes were explored. Growth was studied on substrates oriented by Laue x-ray diffraction between 0.02° and 10° from the {lcub}111{rcub} toward the {lcub}100{rcub}. Terrace growth was observed, with increasing terrace height for larger misorientation angles.; It was found that the purity of the blocking layer was limited by the presence of phosphorus in the lead solvent. Unintentionally doped Ge layers contained ∼1015 cm−3 phosphorus as determined by Hall effect measurements and Photothermal Ionization Spectroscopy (PTIS). Lead purification by vacuum distillation and dilution reduced the phosphorus concentration in the layers to ∼1014 cm −3 but further reduction was not observed with successive distillation runs. The graphite distillation and growth components as an additional phosphorus source cannot be ruled out.; Antimony (∼1016 cm−3) was used as a dopant for the active BIB layer. A reduction in the donor binding energy due to impurity banding was observed by variable temperature Hall effect measurements. A BIB detector fabricated from an Sb-doped Ge layer grown on a pure substrate showed a low energy photoconductive onset (∼6 meV). 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. Sb diffusion into the pure substrate was observed by Secondary Ion Mass Spectroscopy (SIMS) for epilayers grown at 650°C. The Sb concentration at the interface dropped by an order of magnitude over ∼1.5 μm. Layers grown at 550°C did not show significant Sb diffusion.; Sn doped In₂O₃ (ITO) was studied for use in far infrared transparent low temperature contacts for BIB arrays. It was found that ∼100 nm of ITO deposited on Ge remains electrically conducting at 4 K and is ∼90% transparent in the far infrared. ITO should be suitable for passivating contacts to Ge BIB arrays.