Novel mid-infrared silicon/germanium detector concepts

Highly p-doped silicon/silicon-germanium (Si/SiGe) quantum well (QW) struct ures are grown by molecular beam epitaxy (MBE) on double-sided polished [10 0]Si substrates for mid-IR (3 to 5 mum and 8 to 12 mum) detection. The samp les are characterized by secondary ion mass spectroscopy (SIMS), x-ray diff raction, and absorption measurements. Single mesa detectors are fabricated as well as large-area focal plane arrays (FPAs) with 256x256 pixels using s tandard Si integrated processing techniques. The detectors, based on hetero internal photoemission (HIP) of photogenerated holes from a heavily p-doped (p(++) similar to 5x10(20) cm(-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 se tback layers between the highly doped well and the undoped Si layer are int roduced. The temperature dependence of dark currents and photocurrents are measured up to 225 K. in general, we observe broad photoresponse curves wit h peak external quantum efficiencies up to eta (ext) similar to0.5% at 77 K and 4 mu, detectivities up to 8x10(11) cm root Hz/W are obtained. We demon strate that by varying the thickness, Ge content, and doping level of the s ingle- and the multi-QWs of SiGe MIP detectors, the photoresponse peak and the cutoff of the spectrum can be tuned over a wide wavelength range. The e pitaxial versatility of the Si/SiGe system enables a tailoring of the photo response spectrum which demonstrates the advantages of the SiGe system in c omparison over commercially used silicide detectors. (C) 2000 Society of Ph oto-Optical Instrumentation Engineers. [S0091-3286(00)03109-3].