An array of Ag-nGaAs Schottky photodiodes was designed and fabricated with a surface grating to couple incident light into surface plasma waves confined to the air-metal interface. Both electrical and optical characterizations were performed. This device was compared to a similar grating coupled detector consisting of Ag-Ti-nGaAs. The following observations were made concerning (1) the polarization dependent surface plasma enhanced detectivity for 20$\sp\circ$ angle of incidence; (2) the absence of a 24$\sp\circ$ offset experience by the Ag-Ti-nGaAs device; and (3) the improvement in detectivity resulting from the absence of titanium in the Ag-nGaAs device.