Silicon–germanium spherical quantum dot infrared photodetectors prepared by the combination of bottom-up and top-down technologies

By combining a bottom-up, i.e., thermal evaporation method, and the top-down technologies, i.e., molecular beam epitaxy, the spherical SiGe quantum dot infrared photodetectors (QDIP) have been successfully fabricated for the first time. The thermal evaporation method was chosen to synthesize spherical SiGe nanoparticles. They are treated with methanol containing alumina powders in the ultrasonic bath to form a single SiGe dot layer with density about 1.6×1011 cm−2. The QDIP exhibits two response regions, i.e., 1–3.5 and 14–20 μm. The peak responsivity of QDIP is 5.4 mA/W at 2 μm and about 0.6 mA/W at 17 μm at a bias of 200 mV. This QDIP also exhibits photovoltaic response, a short circuit current exists at zero bias. This device is capable of operating up to 240 K with good performance.