In this work, the electrical influence of carbon onW/SiGeC-p/Si(100)-pSchottky diodes is investigated. Analyzed samples consist of fully strained SiGe and SiGeC layers grown by room temperature chemical vapor deposition, deep level transient spectroscopy, (DLTS),I–V,C–V,and secondary ion mass spectroscopy measurements have been carried out. These experiments have shown that carbon incorporation leads to a full depletion of the epitaxial layer. In order to explain this phenomenon, we propose two assumptions: (1) electrical compensation of the active dopant due to a bulk defect, (2) important charge trapping mechanism at the interfaces. Three groups of defects have been detected by DLTS. Their binding energies are respectively 0.21, 0.36 and 0.62 eV above the valence band. Considering the possible origin of these defects, the hypothesises proposed before are discussed.