The potential advantages of the quantum dot infrared photodetectors (QDIPs) as compared with two-dimensional systems are the following [3, 4]: (1) increased sensitivity to normally incident radiation as a result of breaking of the polarization selection rules, so eliminating the need for reflectors, gratings,

or optocouplers, (2) expected large photoelectric gain associated with a reduced capture probability of photoexcited carriers due to suppression GSI-IX of electron-phonon scattering, and (3) small thermal generation rate, resulting from zero-dimensional character of the electronic spectrum, that renders a much improved signal-to-noise ratio. Most of the demonstrations of QDIPs were achieved with III-V self-assembled heterostuctures. SiGe-based QDIPs represent another attractive type of the device due to its compatibility with the standard Si readout circuitry. At present, the most highly developed technology for fabricating arrays of SiGe-based QDs utilizes strain-driven epitaxy of Ge nanoclusters on Si(001) surface [5]. The photoresponse of Ge/Si heterostructures with QDs in the mid-wave atmospheric window was observed by several groups [6–10] and attributed to the transitions

from the hole states bound in Ge QDs to continuum states of the Si matrix. Recently, we have reported on the photovoltaic operation of ten-period Ge/Si(001) QDIPs with Johnson SN-38 noise-limited detectivity as high as 8×1010 cm Hz 1/2/W measured at photon wavelength (λ)=3.4 μm and at 90 K under normal incidence IR radiation [11]. The cutoff

wavelength at the low energy side of the responsivity of such QDIPs was limited to about 5 μm. There are only few works announcing the long-wave operation of detectors based on Ge/Si quantum dots [9, 12–14]. Since the long-wavelength photoresponse in this system originates from the bound-to-bound intraband transitions, superior performance 3-oxoacyl-(acyl-carrier-protein) reductase of such devices is unlikely, and one is obliged to seek another approach. Recently, the fabrication and characterization of a mid-IR QWIP on SiGe pseudosubstrate or virtual substrate (VS) were reported [15]. The use of the pseudosubstrate was found to lead to an increase in design freedom of quantum well devices and thus the possibility to improve their parameters. In this work, we demonstrate that the technologically important range between 8 and 12 μm can be reached by the use of self-assembled Ge QDs grown on the relaxed Si 1−x Ge x layer (x = 0.4). The Ge/SiGe QDIP on SiGe VS displays a A769662 longer cutoff wavelength (approximately 12 μm) and broader detection range as compared to conventional Ge/Si QDIPs due to smaller effective valence band offset at the Ge/Si 1−x Ge x interface. Methods Figure 1 shows schematically the structure of the detector discussed in this paper. The samples were grown by solid source molecular beam epitaxy on a (001)-oriented boron-doped p +-Si substrate with resistivity of 0.