We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : n+-i(QD)-n+ QDIP with undoped quantum dot(QD) active region and n+-n−(QD)-n+ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at 2×1018/cm3. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the n+-n−(QD)-n+ structure, Si dopant is directly doped in InAs QD at 2×1017/cm3. Undoped and doped QDIPs show a photoresponse peak at about 8.3 μm, ranging from 6~10 μm at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

We report the properties of infrared photodetectors based on two kinds of quantum dots(QDs): i) 2.0 ML InAs QDs by the Stranski-Krastanov growth mode(SK QDs) and ii) sub-monolayer QDs by 4 × [0.3 ML/1 nm In0.15Ga0.85As] deposition(SML QDs). The QD infrared photodetector(QDIP) structure of n+-n−(QDs)-n+ is epitaxially grown on GaAs (100) wafers using molecular-beam epitaxy. Both the bottom and top contact GaAs layers are Si doped at 2 × 1018/cm3. The QD layers are grown with Si doping of 2 × 1017/cm3 and capped by an In0.15Ga0.85As layer at 495 oC. The photoluminescence peak(1.24 eV) of the SML QDIP is blue-shifted with respect to that (1.04 eV) of SK QDIPs, suggesting that the electron ground state of SML QDIP is higher than that of the SK QDIP. As a result, the photoresponse regime(~9-14 μm) of the SML QDIP is longer than that (~6-12 μm) of the SK QDIP. The dark current of the SML QDIP is two orders of magnitude smaller value than that of the SK QDIP because of the inserted Al0.08Ga0.92As layer.