Nanoporosity Induced by Ion Implantation in Germanium Thin Films Grown by Molecular Beam Epitaxy

This paper reports on the formation of nanoporous Ge in polycrystalline and amorphous Ge thin films, grown by molecular beam epitaxy and implanted with Ge+ ions at 300 keV with different fluences (3×1015 - 2×1016 Ge/cm2). Implanted polycrystals show a more regular columnar structure with respect to smaller and disconnected voids of amorphous grown films. These results strongly rely on the film properties and mechanism of void nucleation. Our findings represent a goal for the technology transfer of the ion-induced nanoporosity from bulk Ge to Ge thin films and meet the requirements for future applications.