We present an unusual photoconductive response in doped GaAs and InP semico
nductor epitaxial layers and demonstrate that such a response is due to the
longitudinal optic (LO) phonon-induced Fano resonance instead of the tradi
tional kinetic mechanism. Theoretical calculations based upon the present m
echanism are in excellent agreement with the experimental results and the d
eveloped formalism should be universally applicable to the related photocon
ductive processes of other doped semiconductors.