In contradiction with researchers who try to incorporate a maximum of Ge in the channel, we will demonstrate, in spite of a low Ge fraction (15% or 30%) and in spite of the competition between Si-cap and Si1-xGex channels, that we obtain a good trade-off between the gain in drain current, the Si/SiGe interface quality (which is responsible for the mobility reduction by scattering on the interface state and responsible for the drain junction leakage current), and process simplicity. In this article, we also discuss the good quality of the Si1-xGex interface obtained using 15% or 30% Ge. We then propose a new method; directly applicable to the transistor, to study the Si/SiGe interface via admittance spectroscopy.