Evolution of devices for detecting smaller and smaller energy
photons starting from the infrared region of the electromagnetic
spectrum is described. A brief description of the extrinsic
detector development for LWIR to FIR wavelengths is presented.
Several other types of IR detectors including the cutoff
wavelength extension into the FIR range for quantum well infrared
photodetectors (QWIPs) are presented. Efforts in developing p-GaAs Homojunction Interfacial Workfunction Internal Photoemission
(HIWIP) far-infrared detectors and the most recent development in
GaAs/AlGaAs HEterojunction interfacial workfunction internal
photoemission (HEIWIP) far-infrared detectors are also presented.