Influence of surface reconstruction on MBE growth of layered GaSe on Si(111) substrates

Very thin GaSe films, about 100 Å thick, have been epitaxially grown by molecular beam epitaxy on differently ordered Si(111) substrates, namely: the clean 7 × 7 reconstructed surface with its dangling bonds, the H-passivated 1 × 1 surface and the Ga-passivated 3×3R30° reconstructed one. For each substrate, the GaSe layer and its interface with Si have been studied by low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. Upon sequential removal of the GaSe film by Joule heating in ultrahigh vacuum, it is shown that, (i) the band offsets are not sensitive to the initial surface structure of the substrate, (ii) the uniformity of the GaSe layer and of the Fermi level position is questionable on Si(111) 3-Ga, (iii) the density of gap states in the GaSe layer increases upon ageing in air.