The magneto-transport properties of SiGe and SiGeC quantum well structures were studied in relation to their dependence on the growth temperature, Ge and C concentration, well width, and spacer width. It is found that interface roughness and charged impurities are the main origins for scattering in SiGe and SiGeC two-dimensional hole gas (2DHG) structures. Rapid thermal annealing subsequent to growth improves the mobility in SiGeC 2DHG by a factor of 2, whereas only a 20% increase is observed for SiGe 2DHG. At 1.6 K a mobility of 1930 cm(2)/Vs for Si0.81Ge0.185C0.05 and 6900 cm(2)/Vs for Si0.85Ge0.15 channels was deduced from Shubnikov-de Haas oscillations measured up to 8 T. The effective mass determined for holes in the SiGeC alloy is 0.21 +/- 0.02. B delta-doped Si layers were used to determine the B diffusion in the temperature range from 700 to 850 degrees C by intersubband absorption spectroscopy.