Electrical characterizations of Si/SiGe/Si double heterostructures grown by rapid thermal chemical vapour deposition (RTCVD) are carried out to determine the origin of the photoluminescence (PL) intensity decay at low growth temperature (T-G). For the sample grown at the highest T-G, capacitance-voltage measurements show an excellent interface carrier confinement, while deep-level effects are not detected. For the sample grown at the lowest T-G, carrier confinement is less efficient and deep-level transient spectroscopy indicates the presence of both point and extended defects. The apparent activation energy of the deep level related to point defects is close to the heterostructure midgap (E-a = E-v + 0.47 eV). As is shown, the deep level induces an effective non-radiative lifetime of carriers in the SiGe layer which is actually responsible for the SiGe layer photoluminescence degradation at low growth temperatures.