ENHANCED RESPONSIVITY OF HG0.80CD0.20TE INFRARED PHOTOCONDUCTORS USING MBE GROWN HETEROSTRUCTURES

A long wavelength infrared (LWIR) n-type Hg1-xCdxTe photoconductor dev ice (lambda(cutoff) = 14.8 pm) has been developed using two-layer hete rostructures grown by in-situ molecular beam epitaxy (MBE). The experi mental results indicate that incorporating a wider bandgap capping lay er (x = 0.24, 2 mu m thick) on an LWIR absorbing layer (x = 0.20, 10 m u m thick) results in improved responsivity, particularly at higher ap plied bias, when compared with single-layer LWIR detectors. A comprehe nsive device model is used to extract effective contact recombination velocities of 235 cm/s for two-layer photoconductors, and 820 cm/s for single-layer devices, The corresponding excess carrier lifetimes are 0.64 mu s and 0.55 mu s, respectively, compared with the calculated va lue of 1.16 mu s for bulk recombination limited by Auger and radiative mechanisms. The experimental data clearly demonstrates the advantages of employing an MBE-grown Hg1-xCdxTe heterostructure to reduce contac t recombination, and as a technology for forming in-situ grown surface passivation layers. (C) 1997 Elsevier Science B.V.