1. A process for manufacturing a MOS device, comprising: providing a semiconductor layer; forming a gate structure above said semiconductor layer; forming a first doped region within a first surface portion of said semiconductor layer; and irradiating said first doped region with electromagnetic radiation to carry out annealing thereof; wherein forming a dielectric mirror above a second surface portion of said semiconductor layer, prior to said irradiating step, said dielectric mirror being configured to reflect at least in part said electromagnetic radiation.2. The process according to claim 1, wherein forming a dielectric mirror comprises: forming a plurality of pairs of a first mirror layer and a second mirror layer, set on top of one another, said first mirror layer and said second mirror layer having, respectively, a first refractive index and a second refractive index that are different from one another; and etching said first mirror …