Tunneling via impurity states related to the X valley in a thin AlAs barrier

Special features corresponding to resonance tunneling of electrons from the Γ valley of GaAs to the X valley of AlAs were observed in the current - voltage characteristics of single-barrier GaAs/AlAs/GaAs heterostructures. Tunneling both via the states related to the two-dimensional Xxy and Xz subbands and via the related impurity states was detected. It is shown that the energy position of such impurity states is largely controlled by two factors: (i) spatial confinement of the AlAs layer, which influences both the size-quantization energy levels of the Xxy and Xz subbands and the corresponding binding energies of impurity states, and (ii) the biaxial compression of the AlAs layer due to a mismatch of the AlAs and GaAs lattice parameters, which results in the splitting of the Xxy and Xz valleys. This made it possible to determine directly the binding energy of the impurity states; this energy was found to be ∼50 meV for the Xz valley and ∼70 meV for the Xxy valley. © 2001 MAIK "Nauka/Interperiodica".