Self-organized surface nanopatterns on Cd(Zn)Te crystals induced by medium-energy ion beam sputtering

Abstract

Cadmium telluride (CT) and Zn-doped approx 4 at%) CT (CZT) crystals grown by the Bridgman method were mechanically polished to achieve mirror-like surfaces and subsequently irradiated with medium-energy (30–200 keV) Ar⁺ ions under oblique incidence (60° with respect to the target normal). Atomic force microscopy shows that ion sputtering induces the formation of self-organized ripple nanopatterns with wavevector parallel to the ion beam projection on the surface on both CT and CZT targets. The ripple wavelength and amplitude (surface roughness) increase with ion energy. Even with such low doping level, the pattern formation dynamics differs between both materials and, in general, CZT surfaces roughen more easily than CT. In addition, an orthogonal ripple mode develops for extended irradiation, which is more prominent in CZT crystals. Spectroscopic ellipsometry reveals that the C(Z)T crystals have a high radiation hardness since ion bombardment does not induce an amorphized surface layer. This fact also implies that the nanostructured surfaces have significant photoluminescence response, one to two orders of magnitude larger than from as-prepared crystals. These results show that large-area (approx cm²) surface nanostructuring by ion beams can be implemented in the fabrication of future C(Z)T-based devices.