Narrow gap semiconductor photodiodes In this monograph investigations of the performance of narrow gap semiconductor photodiodes are presented and recent progress in different IR photodiode technologies is discussed: HgCdTe photodiodes InSb photodiodes alternatives to HgCdTe III V and II VI ternary alloy photodiodes lead chalcogenide photodiodes and a new class of photodiodes based on two dimensional solids. Investigations of the performance of photodiodes operated in different spectral regions are presented