Intersubband relaxation of two-dimensional electrons in heterostructures.

%'e calculate the lifetime of a nonequilibrium electron in the first excited subband in the lowdensity heterostructure where this photocreated carrier occurs at the last stage of its cooling. The electron interaction with acoustic phonons gives the dominant intersubband relaxation mechanism, if the intersubband energy splitting and the Fermi energy splitting are relatively small, 1 ) e&/Azo ) 0.7—0.8. In GaAs-Al Ga~ As heterostructures the intersubband relaxation determines the excitedelectron lifetime to be of the order of mph nanoseconds mhich depends slightly on the value of the two-dimensional electron density. When the ratio es /Azp is smaller, the intersubband relaxation is determined by the Auger-like electron-electron scattering whose rate can increase up to the value 10 sec