A
photon detector is obtained by using the intersubband absorption mechanism in a modulation doped
quantum well(s). The
modulation doping creates a very high
electric field in the well which enables absorption of input TE polarized light and also conducts the carriers emitted from the well into the modulation doped layer from where they may recombine with carriers from the gate contact. Carriers are resupplied to the well by the generation of electrons across the energy gap of the
quantum well material. The absorption is enhanced by the use of a
resonant cavity in which the
quantum well(s) are placed. The absorption and emission from the well creates a deficiency of charge in the
quantum well proportional to the intensity of the input
photon signal. The quantity of charge in the
quantum well of each
detector is converted to an output
voltage by transferring the charge to the gate of an output
amplifier. The detectors are arranged in the form of a 2D array with an output
amplifier associated with the entire array or a row of the array as in the known charge coupled devices, or a separate
amplifier could be dedicated to each pixel as in the known architecture of the active pixel device. This
detector has the unique
advantage of near
room temperature operation because the
dark current is limited to the generation across the
semiconductor bandgap and not the emission over the
quantum well barrier. The detector also has the
advantage that the readout circuitry is implemented monolithically by the HFETs formed in the GaAs substrate simultaneously, with the detecting elements.