Creation of an antireflection coating for the optical range based on a nanoporous germanium layer formed by implantation with indium ions

The possibility of using a nanoporous Ge layer formed by implantation with $^{115}$In$^+$ ions on a monocrystal $c$-Ge substrate as an antireflection optical coating (In:$P$Ge) was studied. For this purpose, ion implantation of $c$-Ge wafers was performed at an energy $E$ = 30 keV, current density in the ion beam $J$ = 5 $\mu$A/cm$^2$, and dose $D$ = 1.8 $\cdot$ 10$^{16}$ ion/cm$^2$. It was shown that the fabricated In:$P$Ge spongy layer, which consists of intertwining Ge nanowires, is characterized by a low reflectivity ($\sim$5%) in a wide optical spectral range of 250–1050 nm.