STORAGE OF ELECTRONS IN SHALLOW DONOR EXCITED-STATES OF GAP-TE

Tellurium donors in GaP have been ionized by phonon-assisted tunneling in the electric field of pulsed far-infrared laser radiation. In resp onse to the laser pulse a photoconductive signal has been detected wit h a fast component that follows in time the laser pulse and a slow com ponent that rises after the irradiation has ceased and finally exponen tially decays with a strongly temperature-dependent time constant vary ing from several microseconds to milliseconds. It is shown that this t emporal structure of the signal is due to a storage of carriers in the valley-orbit split 1s(E) shallow donor state. Observation of far-infr ared to mid-infrared up-conversion demonstrates that the final step of cascade recombination is achieved by radiative transitions.