Intersubband electroluminescence has been investigated in a quantum cascade structure based on vertical transition designed for far-infrared(&lgr;=88 &mgr;m)emission. A narrow luminescence peak with a full width at half maximum of 0.7 meV is measured at low excitation currents(30 A/cm2) and low temperature(T=5 K).The electroluminescence efficiency exhibits a strong temperature and current dependence, consistent with an interplay between electron–electron and optical phonon scattering. ©1998 American Institute of Physics.