Resonant tunneling photodetector for long wavelength applications

Abstract

A long wavelength detector is formed by coupling a highly doped cathode to an anode through an undoped quantum well or superlattice filter structure. The absorption mechanism is free-carrier absorption in a heavily doped direct bandgap semiconductor (the cathode). The cathode material is preferably chosen such that the conduction band edge is lower than the conduction band edge of the material forming the well of the resonant-tunneling filter. The cathode material should also be semiconductor material of relatively narrow direct bandgap with low effective electron mass. The detector device is biased so that electrons pass through the filter structure by resonant tunneling. To stimulate conduction, incident radiation must have a frequency (i.e., photon energy) sufficient to boost the energy of the cathode electrons from the Fermi energy level of the cathode to the resonance energy level of the quantum-well filter. Thus, photons of incident radiation are absorbed in the cathode which may also be referred to as the photon absorber. In a second, voltage-tunable, embodiment a single quantum well filter having an undoped subband is disposed between a doped cathode and an anode structure. The single quantum well filter structure includes a quantum well with one or more subbands surrounded by two barrier regions. The detection frequency is changed by increasing or decreasing the bias slope of the conduction band which, in turn, moves the quantum well subband energy level relative to the cathode Fermi energy level.