Abstract The photodiode comprises a p+ first layer (19) forming a p-n junction with an n second layer (16). An n third layer (13) disposed on an n+ substrate (11) and epitaxial layer (12) is separated from the second layer by a multiple heterojunction structure formed by fourth n layers (14) alternating with fifth n layers (15). Electrons or holes, whichever have the greater ionization rate are minority carriers in the second layer (16) and majority carriers in the third layer (13) which has a smaller bandgap than the second layer. The fourth layers (14) have a bandgap not smaller than the second layer while the fifth layers (15) have a bandgap not smallerthan the third layer but not larger than the second layer. The structure combines low nosie with high speed.
An avalanche photodiode having a first semiconductor layer (19) Of a first conductivity type, a second semiconductor layer (16) of a second conductivity type adjacent to the first semiconductor layer and wherein electrons or holes, whichever have the greater ionization rate, constitute the minority carrier; a third semiconductor layer (13) of the second conductivity type, having a smaller bandgap than the second layer, wherein electrons or holes, whichever have the greater ionization rate, constitute the majority carrier; and a multi-heterojunction structure between the second and third semiconductor layers and comprising alternating fourth (14) and fifth (15) semiconductor layers of the second conductivity type, the fourth layers (14) having a bandgap not smaller than that of the second layer (16) and the fifth layers (15) having a bandgap not smaller than that of the third layer (13) but not larger than that of the second layer (16).
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