A substrate for a front-side type image sensor includes a supporting semiconductor substrate, an electrically insulating layer, and a silicon-germanium semiconductor layer, known as the active layer. The electrically insulating layer includes a stack of dielectric and metallic layers selected such that the reflectivity of the stack in a wavelength range of between 700 nm and 3 μm is greater than the reflectivity of a silicon oxide layer having a thickness equal to that of the stack. The substrate also comprises a silicon layer between the electrically insulating layer and the silicon-germanium active layer. The disclosure also relates to a method for the production of such a substrate.