Heterojunction far infrared photodetector

A photodetector comprising:

• a. a plurality of N barriers, N being an integer greater than 1, each barrier being a layer of a material made from a first and a second group III elements and a first group V element and characterized by a bandgap;
• b. a plurality of N−1 emitters, each emitter being a layer of material made from a third group III element and a second group V element and characterized by a bandgap different from that of the barriers and having at least one free carrier responsive to optical signals,
• wherein each emitter is located between two barriers so as to form a heterojunction at each interface between an emitter and a barrier, wherein each emitter is doped with a dopant selected from the group consisting of a first group II, IV or VI element to cause free carriers in the emitter, and
• wherein at least one construction parameter of each barrier causes a dark current at least 100 times less than that of a QWIP with the same threshold wavelength at a given temperature.

A photodetector comprising:

• a. at least a first and a second barriers, each barrier being a layer of a first semiconductor material;
• and
• b. at least one emitter, the emitter being a layer of a second semiconductor material different from the first semiconductor material and having at least one free carrier responsive to optical signals,
• wherein the emitter is located between the first and second barriers so as to form a heterojunction at each interface between the emitter and the first and second barriers, and
• wherein the at least one free carrier occupies a range of substantially continuously distributed energies characterized by a three dimensional Fermi level.