A photonic mixer comprising a semiconductor substrate having a field area and means for generating a majority carrier current and an associated electric field in the semiconductor substrate, the semiconductor substrate being doped with a first conductivity type, such that when electromagnetic radiation impinges on the substrate within said field area, pairs of majority and minority carriers are generated in the substrate, resulting in a photocurrent of the minority carriers, said substrate comprising a couple, formed by: - an injecting contact region (3, 4) for injecting the majority carrier current into the semiconductor substrate; and - a detector region (7, 8) for collecting the photocurrent of the minority carriers when said photocurrent being directed towards the injecting contact region (3, 4) by the electrical field associated with the majority carrier current; which injecting contact region (3, 4) is doped with a dopant of the first conductivity type at a higher dopant concentration than the semiconductor substrate; and which detector region (7, 8) is doped with a dopant of a second conductivity type opposite to the first conductivity type and that has a junction (11, 12) with the semiconductor substrate; a zone of the semiconductor substrate around said junction (11, 12) being a depleted substrate zone (101, 102); said couple further comprises a field shaping zone (13, 14) of the first conductivity type extending substantially perpendicularly into the substrate, and having a dopant concentration higher than the dopant concentration of the semiconductor substrate; - the injecting contact region (3, 4) is located, when viewed in a top view, within the field shaping zone (13, 14); the photonic mixer being characterized in that: - either the field shaping zone (13, 14) defines a lateral edge of the couple, laterally surrounds the detector region (7, 8) and is designed to limit the extension of said depleted substrate zone (101, 102) laterally, so that the depleted substrate zone (101, 102) extends more perpendicularly to the substrate surface than laterally, - or the detector region is ring-shaped and extends around the injecting contact region (3, 4), the field shaping zone (13, 14) is a first field shaping zone and the couple further comprises a second field shaping zone (23, 24) of the first conductivity type having a dopant concentration higher than that of the semiconductor substrate, defines a lateral edge of the couple and laterally surrounds the detector region, wherein the field shaping zones (13, 14, 23, 24) are designated to limit the extension of said depleted substrate zone laterally, so that the depleted substrate zone (101, 102) extends more perpendicularly to the substrate surface than laterally. - an injecting contact region (3, 4) for injecting the majority carrier current into the semiconductor substrate; and - a detector region (7, 8) for collecting the photocurrent of the minority carriers when said photocurrent being directed towards the injecting contact region (3, 4) by the electrical field associated with the majority carrier current; - the injecting contact region (3, 4) is located, when viewed in a top view, within the field shaping zone (13, 14); - either the field shaping zone (13, 14) defines a lateral edge of the couple, laterally surrounds the detector region (7, 8) and is designed to limit the extension of said depleted substrate zone (101, 102) laterally, so that the depleted substrate zone (101, 102) extends more perpendicularly to the substrate surface than laterally, - or the detector region is ring-shaped and extends around the injecting contact region (3, 4), the field shaping zone (13, 14) is a first field shaping zone and the couple further comprises a second field shaping zone (23, 24) of the first conductivity type having a dopant concentration higher than that of the semiconductor substrate, defines a lateral edge of the couple and laterally surrounds the detector region, wherein the field shaping zones (13, 14, 23, 24) are designated to limit the extension of said depleted substrate zone laterally, so that the depleted substrate zone (101, 102) extends more perpendicularly to the substrate surface than laterally.