Performance aspects of a quantum-well detector

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Abstract
Calculations of the quantum efficiency and detectivity of an infrared detector based on photoemission from a quantum well are presented. The detector is most efficient when a resonant-extended state exists near the top of the well. The quantum efficiency also increases with increasing electron density. However, due to screening, the absorption peaks at a higher energy than the difference of the energies of the resonant-extended and the bound states by an amount which is proportional to the carrier density in the well. This causes the detectivity (D*) to have a maximum with respect to electron density. We have estimated the dark current and found that, for a GaAs quantum-well detector designed for 10-μm operation, the optimal electron density was 2×1011 cm−2 at 77 K. We have also performed calculations for a quantum-well detector for which the light coupling has been enhanced by incorporating a diffraction grating into the detector. For the stated electron density, we find a D* of 2.8×1011 cm Hz1/2/W and a quantum efficiency of 23%. If the electron density is raised to 8×1011 cm−2, the quantum efficiency rises to 61%, but D* falls to 1.9×1010 cm Hz1/2/W.