Modification of crystalline semiconductor surfaces by low-energy Ar + bombardment: Si(111) and Ge(100)

Abstract

The amorphization of crystalline Si(111) and Ge(100) surfaces induced by low-energy (100 eV to 5 keV) Ar + ion bombardment is studied by means of low-energy electron diffraction (LEED) and electron energy-loss spectroscopy (EELS). The fluences required for the transition from the crystalline into the amorphous state are derived for the (reconstructed) topmost surface layer and the underlying bulk layers. These amorphization fluences increase with decreasing ion impact energy; this variation is most pronounced for energies below ∼ 500 eV and stronger for Ge than for Si. A theoretical formalism based on the general concepts of energy loss for ions penetrating a solid is used to calculate the number of displacements surface and bulk atoms experience due to ion impact. The theoretical results are in good agreement with the experimentally derived amorphization fluences and their energy dependences. Furthermore, they yield a critical defect density in the order of 0.4 for the crystalline-to-amorphous transition for both the surface and the bulk layers, provided a surface displacement energy is chosen which is half of the corresponding bulk value.