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Ballistic-electron-emission microscopy (BEEM) has been used to measure the band structure of both Au/GaAs (001) metal semiconductor (MS) contact and Au/GaAs/AlAs (001) hybrid heterojunction interfaces. Three thresholds have been observed in the BEEM current of the Au/GaAs MS contact, which are attributed to the electron transmission into Γ, L, and X valleys, respectively. The current contribution from the Γ and X valleys is expected since they both can project into the Γ minimum in the (001) direction. However, the contribution from the L valley is somewhat puzzling because the L valley cannot be projected into the Γ minimum. Its contribution to the collector current suggests the possible breakdown of the transverse momentum conservation rule for the interface transmission. We have used Monte Carlo simulation to investigate the detailed behavior of the electron transport in the system. The simulation results agree well with the experiment if the transmission probability is assumed to have a square-root energy dependence, pi∝(V-φi)1/2, for all three valleys, regardless of their projection positions in the (001) direction. For the Au/GaAs/AlAs system, two thresholds which have been identified as electron transmission into the X and L valleys of the AlAs, respectively, were observed. Our Monte Carlo simulations agree with experiment if it is assumed that the electron transmission across the first interface (between Au and GaAs) is noncoherent, i.e., momentum (K) is not conserved, whereas the transmission across the second interface (GaAs/AlAs) is coherent with momentum (K) conserved |
