Jeudi 18 janvier 2001
Narrow potential quantum-wells in semiconductors give rise to the formation of two dimensional electronic states, commonly called subbands. By tailoring the quantum-well widths and the tunnelling barrier thickness which separate the wells, it is possible to create artificial potentials where level separations, matrix elements and lifetimes are mainly dependent on the heterostructure design. This allows to conceive new materials (material by design) where electronic and optical properties can be adapted not only to demonstrate new physical effects, but also to optimise device performances.
Quantum cascade (QC) lasers are an excellent example of how this quantum engineering can be exploited to create functional devices. Their basic principles are completely different from conventional diode lasers, since, in these unipolar devices, there are no transitions across the band gap. It follows that, the emission wavelength depends mainly on the heterostructure design rather than on the constituent materials. To date, QC lasers have been demonstrated in the 4 - 24 mm wavelength region. Room temperature is routinely achieved, with peak power of the order of 1 W in a wide spectral range (5 - 10 mm).
The nature of the QC laser make them not bound to a specific material system and laser action has been already demonstrated in GaInAs/AlInAs lattice matched on InP and on GaAs/AlxGa1-xAs. Very recently we have also observed intersubband electroluminescence (emission in the 3 - 5 mm) in InAs/AlSb heterostructures grown on GaSb. The influence of the different material systems will be presented with a comparative discussion on their role on device performance.