Surface plasmon photodetectors combine metallic features on which surface plasmons may be excited with a semiconductor detector structure such as a pn or Schottky junction. The involvement of surface plasmons in detection conveys particular characteristics to the device, such as enhanced photoyield, polarisation sensitivity or spectral selectivity, which is useful for applications. An application of present interest is the detection of radiation at photon energies below the bandgap energy of silicon, particularly at optical communications wavelengths (1310 and 1550 nm), targeting optical interconnect and sensing applications. Internal photoemission on metal-silicon Schottky contacts is well-suited for this purpose as it is a broadband detection mechanism (optical and electrical). Internal photoemission is inefficient but structuring the metal forming the Schottky contact to excite surface plasmons at the metal-semiconductor interface results in an enhancement of the responsivity of the detector. Structures that exploit surface plasmons to enhance photodetection are discussed.