Raman study of germanium nanowires formed by low energy Ag⁺ ion implantation

Abstract

Porous Ge layers of nanowires were formed by low energy (30 keV) Ag+ ion implantation of crystalline c-Ge substrate. Different radiation doses resulted in the formation of nanowires with various mean diameters. The obtained layers were studied by Raman spectroscopy using helium-neon and argon exciting lasers at wavelength of 633 and 488 nm respectively. It was demonstrated that implanted amorphous layers were locally crystallized by the lasers. The crystallization thresholds were found to be 3 kW/cm2 for helium-neon exciting laser and 1 kW/cm2 for argon exciting laser. The variation of thresholds is suggested to be due to the different light penetration depths at these wavelengths in Ge. The crystalline volume fraction was determined and reached maximum value of 6–7%, the divergence of which can be explained by the difference in the distribution of Ge nanowire diameters.