Efficient, high-bandwidth organic multilayer photodetectors

Organic photodetectors incorporating an ultrathin (greater than or equal to 5 Angstrom) donor-acceptor alternating multilayer stack as the optically a ctive region exhibit external quantum efficiencies of 75% across the visibl e spectrum, and have subnanosecond response times. Photogenerated excitons efficiently dissociate into free electrons and holes by rapid charge-transf er across the several closely spaced organic-layer interfaces. The dependen ce of the quantum efficiency on applied voltage and layer thickness suggest s that escape of photogenerated carriers from potential wells formed by the multilayers due to tunneling prior to recombination leads to the high effi ciencies observed. The impulse response of the highest-bandwidth devices is characterized by a full width at half maximum of (720 +/- 70) ps. The perf ormance of these devices makes them a useful building block for molecular o rganic photonic integrated circuits. (C) 2000 American Institute of Physics . [S0003-6951(00)02826-6].