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Highly p-doped Si1-xGex quantum well (QW) layers have been grown by molecular beam epitaxy (MBE) on <100> silicon (Si) for detectors in the mid-infrared regime (3 (mu) - 5 (mu) , 8 (mu) - 12 (mu) ). The 5 nm - 10 nm thick SiGe QW layers were boron doped up to 5 1020 cm-3 with Ge contents of 0.4 less than or equal to x less than or equal to 0.5 and have been pseudomorphically deposited on undoped Si. The principle of detection is by hetero-internal photoemission (HIP) across the Si/SiGe valence band barrier. This sequence has been repeated up to ten times and the structure has been terminated with a p-doped SiGe contact layer on top. The structure of the grown samples have been extensively analyzed by secondary ion mass spectroscopy (SIMS), x-ray diffraction (XRD), Rutherford backscattering (RBS) and absorption spectroscopy. Mesa detectors of varying diameters have been fabricated using standard Si processing techniques, and the photocurrent and dark current have been measured at 77 K. A maximum quantum efficiency of (eta) ext equals 1.4% has been achieved (at 4 (mu) and 77 K) with dark current densities of 10-5 A/cm2, the spectral dependence of the photoresponse showed a broad maximum between 3 (mu) and 5 (mu) . Different layer designs with repeated quantum wells and varying doping levels and Ge content in the well have been studied theoretically and experimentally to optimize the structure with respect to high responsivity and low dark current.
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