A photonic structure comprising: a photo detector (134,170) having a first interface between a light receiving region and a first semiconductor region which is part of a substrate, the first interface having a crystalline lattice mismatch between the light receiving region and first semiconductor region; a waveguide core for supplying optical signals to the light receiving photo detector at a location within the light receiving region which is elevationally displaced from the interface; and an isolation region formed at least partially in the substrate and having an upper surface at a higher elevational level than an upper surface of the substrate, the waveguide core being located on the upper surface of the isolation region and the first interface being located at the upper surface of the substrate, wherein the light receiving region comprises an intrinsic region and the first semiconductor region has a first type of conductivity, wherein the photo detector further comprises a second semiconductor region and a second interface between the intrinsic region and second semiconductor region, the second semiconductor region having a second type of conductivity, and wherein the photonic structure further comprises an oxide layer provided over the waveguide core and substrate, the oxide layer comprising an opening, the photo detector intrinsic region being formed in the opening of the oxide layer, the second semiconductor region being formed in the opening over the intrinsic region, wherein the opening has an upper portion and a lower portion, the upper portion being wider than the lower portion. a photo detector (134,170) having a first interface between a light receiving region and a first semiconductor region which is part of a substrate, the first interface having a crystalline lattice mismatch between the light receiving region and first semiconductor region; a waveguide core for supplying optical signals to the light receiving photo detector at a location within the light receiving region which is elevationally displaced from the interface; and an isolation region formed at least partially in the substrate and having an upper surface at a higher elevational level than an upper surface of the substrate, the waveguide core being located on the upper surface of the isolation region and the first interface being located at the upper surface of the substrate, wherein the light receiving region comprises an intrinsic region and the first semiconductor region has a first type of conductivity, wherein the photo detector further comprises a second semiconductor region and a second interface between the intrinsic region and second semiconductor region, the second semiconductor region having a second type of conductivity, and wherein the photonic structure further comprises an oxide layer provided over the waveguide core and substrate, the oxide layer comprising an opening, the photo detector intrinsic region being formed in the opening of the oxide layer, the second semiconductor region being formed in the opening over the intrinsic region, wherein the opening has an upper portion and a lower portion, the upper portion being wider than the lower portion.