Terahertz quantum cascade structures: Intra- versus interwell transition

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