Photodiodes as Optical Radiation Measurement Standards

Photodiodes for optical radiation measurements are used without reverse bias in most ap‐ plications since this operation yields the lowest dark current. To obtain photodiodes that op‐ erate at a low bias and have a low dark current, it is necessary to produce epitaxial layers that are pure and have few defects (such as dislocations, point defects, and impurity precipi‐ tates). Furthermore, a planar device structure requires that a guard ring be used to keep the electric field around the photoreceptive area from increasing too much. Fabrication and processing technologies such as impurity diffusion, ion implantation, and passivation play important roles in the production of reliable photodetectors.