KEYWORDS: Quantum chromodynamics, Transition metals, Quantum efficiency, Absorption, Sensors, Electric field sensors, Doping, Modulation, Quantum wells, Electron transport
This work proposes a novel way to regulate the electron quantum states of quantum cascade detectors (QCDs) by utilizing localized built-in electric field introduced by modulation doping. The mechanism that how the localized built-in electric field influences extraction efficiency is studied by analyzing the quantum transitions in a simplified three-quantum-well model. The calculation results show that, by introducing the localized built-in electric field, a transition energy close to the LO phonon energy can be more easily realized with almost unchanged transition matrix element. The transition matrix element can be enlarged by the localized built-in electric field with almost unchanged transition energy. The calculated extraction efficiency is below 65% for the standard QCD structures without localized built-in electric field, whereas for the structures with localized built-in electric field, the extraction efficiency can reach above 80%. From experimental results, a higher extraction efficiency of photo-generated electrons of 89% is obtained for the proposed QCD structure, comparing with 63% for the standard QCD structure. The peak response wavelengths of two structures are both around 4.5 μm. At temperatures ranging from 40K to 210K, the photocurrents of the structure with localized built-in electric field are over 55% larger than those of the standard structure. To sum up, the localized built-in electric field can be utilized to regulate the electron states besides the layer thickness and material composition of QCDs.
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