Abstract
Highly p-doped silicon/silicon-germanium (Si/SiGe) quantum well (QW) structures are grown by molecular beam epitaxy (MBE) on double-sided polished <100)Si substrates for mid-IR (3 to 5 ?m and 8 to 12 ?m) detection. The samples are characterized by secondary ion mass spectroscopy (SiMS), x-ray diffraction, and absorption measurements. Single mesa detectors are fabricated as well as large-area focal plane arrays (FPAs) with 256x 256 pixels using standard Si integrated processing techniques. The detectors, based on heterointernal photoemission (HIP) of photogenerated holes from a heavily p-doped (p+ + ~5x 1020cm-3) SiGe QW into an undoped silicon layer, operate at 77 K. Various novel designs of the SiGe HIP's such as Ge- and B-grading, double- and multi-wells, are realized; in addition, thin doping setback layers between the highly doped well and the undoped Si layer are introduced. The temperature dependence of dark currents and photocurrents are measured up to 225 K. In general, we observe broad photoresponse curves with peak external quantum efficiencies up to next ~0.5% at 77 K and 4?, detectivities up to 8x 1011 cm?Hz/W are obtained. We demonstrate that by varying the thickness, Ge content, and doping level of the single- and the multi-QWs of SiGe HIP detectors, the photoresponse peak and the cutoff of the spectrum can be tuned over a wide wavelength range. The epitaxial versatility of the Si/SiGe system enables a tailoring of the photoresponse spectrum which demonstrates the advantages of the SiGe system in comparison over commercially used silicide detectors.
