The local crystallization thresholds under laser irradiation of the Cu+-ion implanted Ge layers with various thicknesses

Porous Ge layers were fabricated by implanting Cu+ ions of various acceleration energies into c-Ge substrate. This made it possible to form amorphous porous Ge layers of thicknesses from 18.6 to 50.5 nm. The distribution depth profiles of implanted Cu+ ions in Ge were simulated by SRIM-2013 program. The formed layers were studied by Raman spectroscopy. The excitation was carried out by a laser with a wavelength of 488 nm, which has a small penetration depth of similar to 20 nm. In the Raman spectra, there is a possibility to distinguish the contribution from the amorphous Ge film, the crystalline c-Ge substrate, and Ge nanocrystals, which appear under intense laser excitation due to local crystallization. The decomposition of the spectra into individual components makes it possible to subtract the contribution of the substrate and estimate the crystalline volume fraction in the layers. The results obtained confirm the hypothesis of low thermal conductivity of the porous layer, due to which local crystallization occurs.