Formation of nanoporous germanium layers on thin films obtained by ion-assisted deposition

The present study is aimed to test a possibility for formation of nanoporous Ge-PGe layers by implantation with Ag$^+$ ions thin amorphous film $a$-Ge obtained by the original method of ion-stimulated deposition. For this purpose, a $c$-Ge target was sputtered with low-energy Xe$^+$ ions onto a quartz glass substrate coated with a conductive Ni layer. Ion implantation was performed at an energy of $E$ = 30 keV, a current density of $J$ = 5 $\mu$A/cm$^2$ and doses of $D$ = 2.0 $\cdot$ 10$^{16}$ and 6.0 $\cdot$ 10$^{16}$ ion/cm$^2$. Electron microscopy and optical reflectance spectroscopy were used to analyze the formed material. It is shown that at a low implantation dose the film surface remains smooth, whereas an increase in the dose leads to the formation of a nanoporous Ge layer consisting of needle-like structures randomly located in the plane of the sample surface.