Reduced dimensionality of hot-carrier relaxation in GaAs quantum wells

Cooling of hot electron-hole plasmas in GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum wells of varying width is investigated by picosecond luminescence spectroscopy. The energy loss via Fröhlich interaction is at low plasma density independent of dimensionality and well width and close to theoretical expectation; its rate decreases sharply with increasing excitation density. Areal excitation density, rather than volume density, is shown to be the relevant variable, which indicates reduction of phase-space dimension for the coupled carrier-phonon system.