HOT-ELECTRON TRANSPORT THROUGH AU GAAS AND AU/GAAS/ALAS HETEROJUNCTION INTERFACES - BALLISTIC-ELECTRON-EMISSION-MICROSCOPY MEASUREMENT AND MONTE-CARLO SIMULATION/

Ballistic-electron-emission microscopy (BEEM) has been used to measure the band structure of both Au/GaAs (001) metal semiconductor (MS) con tact and Au/GaAs/AlAs (001) hybrid heterojunction interfaces. Three th resholds have been observed in the BEEM current of the Au/GaAs MS cont act, which are attributed to the electron transmission into Gamma, L, and X valleys, respectively. The current contribution from the Gamma a nd X valleys is expected since they both can project into the Gamma mi nimum in the (001) direction. However, the contribution from the L val ley is somewhat puzzling because the L valley cannot be projected into the Gamma minimum. Its contribution to the collector current suggests the possible breakdown of the transverse momentum conservation rule f or the interface transmission. We have used Monte Carlo simulation to investigate the detailed behavior of the electron transport in the sys tem. The simulation results agree well with the experiment if the tran smission probability is assumed to have a square-root energy dependenc e, p(i) proportional to(V - phi(i))(1/2) for all three valleys, regard less of their projection positions in the (001) direction. For the Au/ GaAs/AlAs system, two thresholds which have been identified as electro n transmission into the X and L valleys of the AlAs, respec tively, we re observed. Our Monte Carlo simulations agree with experiment if it i s assumed that the electron transmission across the first interface (b etween Au and GaAs) is noncoherent, i.e., momentum (K) is not conserve d, whereas the transmission across the second interface (GaAs/AlAs) is coherent with momentum (K) conserved.