Semiconductor photonics devices for coupling radiation to a semiconductor waveguide are described. An example photonics device comprises a semiconductor-on-insulator substrate comprising a semiconductor substrate, a buried oxide layer positioned on top of the semiconductor substrate, and the semiconductor waveguide on top of the buried oxide layer to which radiation is to be coupled. The example device also comprises a grating coupler positioned on top of the buried oxide layer and configured for coupling incident radiation to the semiconductor waveguide. The semiconductor substrate has a recessed portion at the backside of the semiconductor substrate for receiving incident radiation to be coupled to the semiconductor waveguide via the backside of the semiconductor substrate and the grating coupler.