Terahertz electroluminescence originating from spatially indirect intersubband transitions in a GaAs/AlGaAs quantum-cascade structure

The terahertz electroluminescence of a GaAs/AlGaAs quantum-cascade structure in the range ∼33–60 cm−1 (1–1.8 THz) is studied and an energy-level diagram of the structure is calculated. The strongest transitions in this system are analyzed and their dependence on the applied electric field is investigated. The analysis indicates that the observed line of terahertz radiation can be related to spatially indirect transitions of electrons between the states localized in neighboring quantum wells and corresponding to the minima in the quantum-confinement subbands. The results of numerical simulations satisfactorily describe the spectral position of the electroluminescence line and its shift as the bias voltage increases across the quantum-cascade structure.