Compensation of charge fluctuations in quantum wells with dual tunneling and photon-assisted escape paths

In our previous article [D. H. Huang, A. Singh, and D. A. Cardimona, J. Appl. Phys. 87, 2427 (2000)], we explained the experimentally observed zero-bias residual tunneling current [A. Singh and D. A. Cardimona, Opt. Eng. 38, 1424 (1999)] in quantum-well photodetectors biased by an ac voltage. In this article, we extend our theory to include the photoemission current and reproduce our recent findings on the dynamical drop of photoresponsivity R-ph(t) from its static value R-ph(0) in quantum-well photodetectors as a function of the chopping frequency of the incident optical flux. In this theory, we derive a dynamical equation for a nonadiabatic space-charge field E-na(t) in the presence of an applied electric field E-b(t) and an incident optical flux Phi (op)(t). From it, a compensation of the charge fluctuations in quantum wells is predicted as a result of dual tunneling and photon-assisted escaping paths. We also find a suppression of the nonadiabatic deviation of R-ph(t) from R-ph(0) due to a charge-depletion effect in the quantum wells. (C) 2001 American Institute of Physics.