Diffraction Grating Based on Implanted Layers of Nanoporous Germanium

Abstract

The present study is devoted to a new technique for creating diffraction gratings based on nanoporous Ge (PGe) layers by irradiating a smooth single-crystal c-Ge (Bi:PGe) substrate with Bi⁺⁺ ions through a copper mesh mask at an energy of E = 72 keV, an ion beam current density of J = 5 μA/cm², and a fluence D range from 1.3 × 10¹⁵ to 1.3 × 10¹⁷ ion/cm² with the ILU-3 ion accelerator. Morphological and elemental analyses of the Bi:PGe surface for different D values were performed using a high-resolution scanning electron microscope. At D = 1.3 × 10¹⁵ ion/cm², the formation of a porous fraction in the form of vertical honeycombs with nm-sized round holes was detected. When the critical value D = 3.1 × 10¹⁵ ion/cm² is exceeded, a spongy porous structure consisting of intertwining nanowires appears, accompanied by swelling of the Bi:PGe layer instead of the expected sputtering of the c-Ge surface. With increasing D, the nanowires become thinner and the free volume between them increases. The formation of periodic Bi:PGe microstructures on the c-Ge surface was monitored using optical and probe microscopy. The efficiency of the optical diffraction grating was demonstrated by probing it with He–Ne laser radiation.