Patent ID: 7253432

Claim:
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; and 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 emitter causes at least one free carrier to occupy a range of substantially continuously distributed energies characterized by a three dimensional Fermi level and respond to optical signals having wavelength in the range of 3 to 100 μm with significant absorption.