Opto Diode introduced the 20 mm2 photodiode with a circular active area that is ideal for electron detection. The new device offers 100% internal quantum efficiency (QE) and increased stability. The absence of a surface dead region results in 100% collection efficiency. The radiation-hard, junction-passivating, oxynitride protective entrance window makes the device extremely stable even after exposure to intense flux of UV photons (showing less than 2 percent responsivity degradation after megajoules/cm2 of 254 nm and tens of kilojoules/cm2 of 193 nm photon exposure). The exceptional radiation-hardness makes these diodes much better suited than conventional silicon photodiodes for space missions and/or satellite applications.