Experimental determination ofΓ−Xintervalley transfer mechanisms in GaAs/AlAs heterostructures

Zone-center-zone-boundary ($\Gamma -X$) intervalley transfer mechanisms in AlAs/GaAs heterostructures are deduced in an unambiguous way from transport and electroluminescence studies of single-AlAs-barrier diodes. We demonstrate that the tunneling is strongly sequential and depends on the nature of the $X$ state involved. For $X_z$ the transfer is mainly elastic, whereas momentum conserving phonon assistance is dominant for $X_{\mathrm{xy}}$. Quantitative values for the scattering rates for each transfer mechanism are obtained. The conduction-band offset from the $\Gamma$ minimum in GaAs to the $X$ minimum in AlAs is shown to be only 120±6 meV.