Near-field coupling effect in normal-incidence absorption of quantum-well infrared photodetectors

Experiments have shown a significant photoresponsivity in quantum well (QW) infrared photodetectors (QWIP) with normal incidence without optical grating. Different explanations based on the energy band structures have been given, but no concrete conclusions can be drawn at the present stage. We develop a theory based on the optical near-field effect in the QW active region to explain the observed photoresponsivity in the normal incidence condition. Our theory indicates that the near-field effect results in an evanescent wave which induces a nonzero electrical component in the optical field along the QWIP growth direction in the quantum well region inducing the observed photoresponsivity. (C) 1999 American Institute of Physics. [S0021-8979(99)08102-5].