Terahertz quantum cascade structures: Intra- versus interwell transition

Terahertz quantum cascade structures (emission around 20 meV) based on intr a- and interwell transitions have been compared in magnetotransport and int ersubband-electroluminescence experiments. The interwell transition exhibit s a Stark shift of up to 6 meV. We also observe a smaller energy shift of t he intrawell transition which is attributed to the tunnel splitting, when t he initial and final subbands mix with those of the injectors. The electric field induced narrowing of the emission line and our band structure calcul ations support this interpretation. The quantum efficiency of the electrolu minescence is of similar magnitude for the two transitions, despite their l arge difference in the spatial subband overlap. (C) 2000 American Institute of Physics. [S0003-6951(00)03739-6].