Epitaxial crystallization and nucleation during MeV-ion beam processing of amorphous GaAs surface layers

<100> -GaAs wafers were preamorphized in a thin surface layer using 50 keV 14N+-ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) were studied as a function of the target temperature using MeV Ar+- or Kr+-ions. Backscattering experiments and electron microscopy show that the IBIEC process is stopped above a critical irradiation temperature due to enhanced ion beam induced nucleation and growth of crystallites. At a fixed dose an optimum irradiation temperature for IBIEC was found, at which the recrystallized layer thickness has a maximum and crystallite formation is negligible. This offers the possibility to crystallize much larger layer thicknesses than ∼65 nm which stands for the maximum value reported up to now. (orig.)