Silicon nanocone formation via low-energy helium ion sputtering

Abstract

In this study, the effect of low-energy (100 eV) He+ ion irradiation on Si surface morphology is explored. Si (100) and (111) samples were irradiated with 100 eV He+ ions at an elevated sample temperature of 600 °C and to fluences in the range 5.0 × 1019–2.0 × 1020 ions cm–2. Through a combination of high ion flux and high sample temperature, it was found that continued He+ ion irradiation facilitates the formation of homogeneously populated, high aspect ratio silicon nanocones (NCs) (∼50–100 nm base and ∼200–400 nm height). The resulting surface morphology is shown to have excellent antireflective properties, suggesting potential application toward enhanced light absorption in photovoltaic and other optical applications. Furthermore, similar irradiations at reduced sample temperature show comparable structuring mechanisms but with smaller cone diameter. These results indicate that NC size and number density (and related wavelength-dependent reflectivity properties) may be tailored by carefully tuning ion irradiation conditions. Utilizing very low-energy He+ ions as the irradiating species, these studies also demonstrate an added benefit to limiting metallic surface contamination through reduced probability of sputtering in-vacuum components.