A comparison between BEEM currents on Au/Si(1 1 1) and Au/Si(1 0 0): inelastic and geometrical effects

Using a Keldysh Greenʹs function formalism we have theoretically studied ballistic electron emission microscopy BEEM currents through Au/Si(1 0 0) and Au/Si(1 1 1) structures as a function of Au thickness. Our analysis shows that for thin films, BEEM current is greater for Si(1 0 0) than for Si(1 1 1) substrates; however, in the case of thick films (more than 15 nm) the BEEM current associated with the Si(1 1 1) orientation is greater, in agreement with recent experimental data. This behaviour is due to the change in the symmetry of the k-space current distribution after the electrons propagate through the Au lattice, changing from a sixfold symmetry (which favours the matching with Si(1 0 0) available states) to a threefold one as thickness increases. Moreover, we have analysed how the relative alignment of the metal and the semiconductor affects the final BEEM current. All these results show that taking into account the band structure of the metallic layer is essential for a detailed understanding of the transport process.