Pseudomorphic Si1-xGex single layers and Si1-xGex/Si multiple quantum wells (MQWs) were successfully grown on Si(100) wafers at low temperatures (440-510 degrees C) by an ultra-high-vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) technique. Growth kinetics of UHV-ECRCVD was reported, and the unique influence of hydrogen plasma on the growth process was discussed. Transmission electron microscopy (TEM) was used to investigate the structural quality of Si1-xGex single layers and MQWs. It was shown that the Si1-xGex/Si MQWs were foe of extended defects, fully strained, and maintained good uniformity of thickness. Double axis rocking curves and reciprocal space maps by triple axis X-ray diffraction were employed to extract structural parameters from the samples. Interfaces were flat and coherent, and no appreciable tilts or mosaic spreading were observed. It was demonstrated that UHV-ECRCVD is suitable for low-temperature growth of quantum structures with high structural quality.