Terahertz-electroluminescence in a quantum cascade structure

We report on spontaneous terahertz emission from a quantum cascade structur e, based on carrier injection into the excited state of a 26 nm quantum wel l. We have measured luminescence at a photon energy of 17.3 meV with a full line-width at half-maximum of 1.3 meV. Comparing the outcoupling efficienc y from differently processed samples, we observe a higher signal from the e dge emission of ridges than from grating coupled surface emission. The spec troscopy on cleaved facet waveguide resonator samples grown on a semi-insul ating substrate reveals a significant reduction of absorption in the substr ate. (C) 1999 Elsevier Science B.V. All rights reserved.