Germanium Blocked Impurity Band Detectors

Ge:Sb BIB detectors have been fabricated by growing an Sb doped IR active layer (typically 40 micrometers) on pure Ge <111> oriented substrate wafers by Liquid Phase Epitaxy (LPE) from a Pb solution, and thinning the pure wafer to a thickness of 10 micrometers. Extended long wavelength response to ~ 50 cm-1 which rapidly increases with bias has been observed in Ge:Sb BIB detectors with Nd ~ 1 x 1016 cm-3. The responsivity at long wavelengths is lower than expected. This can be attributed to Sb diffusion from the IR active layer into the blocking layer during LPE growth. BIB modeling indicates that this Sb concentration profile increases the electric field in the transition region and reduces the field in the blocking layer. A minority acceptor concentration of ~ 2 x 1012 cm-1 was determined by Hall effect and C-V measurements on a BIB device, corresponding to an estimated depletion width ~ 1.5 micrometer.