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 ${\mathcal{R}}_{\mathrm{ph}}\mathrm{(t)}$ from its static value ${\mathcal{R}}_{\mathrm{ph}}^0$ 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 ${\mathcal{E}}_{\mathrm{na}}\mathrm{(t)}$ in the presence of an applied electric field ${\mathcal{E}}_b\mathrm{(t)}$ and an incident optical flux ${\Phi }_{\mathrm{op}}\mathrm{(t).}$ 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 ${\mathcal{R}}_{\mathrm{ph}}\mathrm{(t)}$ from ${\mathcal{R}}_{\mathrm{ph}}^0$ due to a charge-depletion effect in the quantum wells.