We study interaction of single-electron current and incident photons in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors. Trapping events of a photoexcited-electron by a trap donor are observed as random telegraph signals in single-electron-tunneling current flowing through a current-path donor. Trapping causes a potential change at the current-path donor, inducing a current change. An opposite current change is caused by electron detrapping from the trap donor to the current-path donor. This indicates that only a few donors (two donors in this study) work in the interaction between single-electron transport and photoexcited-electron trapping, even in the presence of many donors.