Ion Implantation: Nanoporous Germanium

The formation of amorphous thin surface layers of nanoporous Ge with various morphologies during the low-energy high-dose implantation by metal ions of different masses, namely ⁶³Cu⁺, ¹⁰⁸Ag⁺, and ²⁰⁹Bi⁺, on single-crystal c-Ge substrates was experimentally demonstrated using high-resolution scanning electron microscopy. The structure of the obtained nanoporous Ge layers was studied using backscattered electron diffraction. Under irradiation with low-energy ions, such as ⁶³Cu⁺ and ¹⁰⁸Ag⁺, needle-like nanostructures constituting a nanoporous thin Ge layer form on the surface of c-Ge. However when employing havier ²⁰⁹Bi⁺, the implanted layer consists of densely packed nanowires. At high ion-irradiation energies, the morphology of the thin surface layers of nanoporous Ge undergoes a sequential transformation in shape from three-dimensional reticulated to spongy as the mass of the implanted ions increased. Such a spongy structure was formed by sparse individual intertwining nanowires. The general potential mechanisms for pore formation in Ge during low-energy high-dose ion implantation are discussed, including the cluster–vacancy mechanism, local thermal microexplosion, and localized heating accompanied by surface melting with effective sputtering.