A metal-semiconductor-metal (MSM) device couples light from an optical mode in a waveguide to a surface plasmon polarition (SPP) mode on an electrode surface of the MSM device. Once in an SPP mode, the absorption of light in the semiconductor can take place in a very small area. This may allow for a shrinking of the active detector area and allow for low capacitance, very short transit distance for the electrical carriers and allow for very low voltage devices and/or very high frequency.