Resonant Γ-X tunneling in single-barrier GaAs/AlAs/GaAs heterostructures

The electron transport through single-barrier GaAs/AlAs/GaAs heterostructures is studied. This transport is caused by resonant tunneling between the two-dimensional states related to the Γ valley of the GaAs conduction band and various two-or zero-dimensional donor states related to the lower X valleys of the AlAs conduction band. The resonant electron tunneling both via various two-dimensional states related to the Xz and Xxy valleys in AlAs (the Xz and Xxy states) and via related states of Si donors X z D and X xy D was observed. This circumstance made it possible to determine the binding energies of these states (EB(X z D )≈50 meV and EB(X xy D )≈70 meV, respectively) directly from the results of identification of resonance features in transport characteristics. An analysis of the structure of experimental resonances corresponding to tunneling between the Γ and X Landau levels in a magnetic field made it possible to determine the transverse effective mass in the X valleys of AlAs (mt=(0.2±0.02)m0). An additional fine structure of donor resonances is observed in experimental transport characteristics. This fine structure is caused by resonant tunneling of electrons through the states of the donors that are located in various atomic layers of the AlAs barrier (in the growth direction) and therefore have different binding energies.