Narrowing of the intersubband electroluminescent spectrum in coupled-quantum-well heterostructures

We show that the introduction of a setback between the active region and the dopants has a dramatic effect on the spectrum of quantum-well intersubband electroluminescence at cryogenic temperatures, namely a strong blue shift and narrowing of the emission line. This is accompanied by a change of line shape from Gaussian to Lorentzian. A remarkable electric-field induced narrowing of the electroluminescent spectrum down to a width of 21 meV is also observed.