We demonstrate mid-infrared emission from cascade structures based on InAs quantum dashes (QDashes) grown on tensile-strained AlInAs. The proposed design relies on a diagonal transition from the QDash ground state to the following quantum well. The measured electroluminescence is very broad and tunes strongly with the applied voltage. A comparison with an identical structure, where the dashes were replaced by a lattice-matched InGaAs quantum well (QW), shows quite different transport properties. A sharp alignment between the injector and the optical transition upper state is present in the QW sample, while the alignment is smoother in the QDash one. Moreover, the QW device exhibits a negative differential resistance not present in the QDash one. This can be attributed to the inhomogeneous nature of the QDashes. Decreasing the tunneling barrier between the QDashes and the following QW increases the injected current as does increasing the doping in the active region. A gain extrapolation from our electroluminescence measurements shows that these structures are promising for the development of quantum cascade lasers based on a 3D confined active region. (C) 2010 Elsevier B.V. All rights reserved.