Terahertz-quantum-cascade emitters: interwell versus intrawell transitions

Summary form only. In the course of the development of a quantum cascade laser emitting terahertz radiation, two different designs of the active region have been proposed. One of them employs an intrawell radiative transition between the two lowest subband of a wide quantum well, the other one an interwell transition between the ground subbands of two adjacent wells. In our study, we experimentally investigate the dependence of the frequency, the linewidth and the efficiency of the spontaneous emission on the spatial overlap of the initial and final subbands. We present measurements of intersubband electroluminescence on three different AlGaAs-GaAs quantum cascade structures.