Heteroepitaxial growth of the intrinsic vacancy semiconductor Al₂Se₃ on Si(111): Initial structure and morphology

The evolution of nanostructure morphology and local chemical environment during heteroepitaxial growth of aluminum selenide on Si(111) was investigated with scanning tunneling microscopy and high-resolution photoemission spectroscopy. Despite the strong similarity to GaSe in atomic and electronic structure during deposition of the first AlSe bilayer, subsequent growth is quite different—resulting in an alternating Al-Se-Al-Se stacking sequence consistent with defected-wurtzite-structure Al₂Se₃. The first bilayer is completed on a given terrace before the second layer nucleates, but subsequent layers nucleate before completion of the second layer. The surfaces of well-formed Al_xSe_y islands are smooth and terminated by Se atoms; Al then sticks before additional Se, resulting in rougher incomplete islands with Al-rich disordered surfaces. Growth with extra Al in the incident flux does not result in layered AlSe and induces only subtle differences in film morphology.