Simulations of Ge+ and C+ implantations in Si were performed to study bandgap grading in the SiGeC/Si heterojunction bipolar transistor (HBT). Although no bandgap discontinuity was observed at the base-emitter junction, it was found that a wide-bandgap emitter and a narrow-bandgap base with proper bandgap grading were obtainable with implantation. Electrical characterization of SiGe and SiGeC diodes formed by Ge+ and C+ implantations in Si was carried out. Current-voltage (I-V) measurement results confirm that carbon doping improves the crystalline quality of the germanium-implanted layer. On the other hand, capacitance-voltage (C-V) measurements indicate that both germanium and carbon implantations result in considerable dopant deactivation.