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 heteoepitaxial 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 before additional growth, but subsequent layers nucleate before completion of the second layer. The surfaces of well-formed AlxSey islands are smooth, and terminated by Se atoms, with Al then sticking 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, but rather increases the average Al2Se3 island size.