Comparisons of vacuum surface effects on commercial photodiodes: spatial response uniformity via a computerized laser...

A computerized electrooptics scanning system was used to spatially map active area photoresponse uniformity of various commercial photodiodes under 1-atm air and 10(-3)-Torr vacuum conditions. The automated measurement apparatus includes computer, optical, mechanical, and electrical systems. It has been found that vacuum operation improves the overall quantum efficiency of the detectors up to 18% (RCA 30180), increases the effective detection area, and affects surface uniformity. A hypothesis is presented to explain these changes induced from surface effects. Under vacuum operation, surface ionic charges, which induce surface electric field, are affected. This induced electric field affects the overall quantum efficiency. Surface recombination velocity and gap energy states can also be affected by vacuum operation, hence affecting the quantum efficiency.