CdTe Nanowires by Au-Catalyzed Metalorganic Vapor Phase Epitaxy.

Abstract

We report on the first Au-catalyzed growth of CdTe nanowires by metalorganic vapor phase epitaxy. The nanowires were obtained by a separate precursors flow process in which (i) di-isopropyl-telluride (ⁱPr₂Te) was first flowed through the reactor to ensure the formation of liquid Au-Te alloy droplets, and (ii) after purging with pure H₂ to remove unreacted ⁱPr₂Te molecules from the vapor and the growth surface, (iii) dimethylcadmium (Me₂Cd) was supplied to the vapor so that Cd atoms could enter the catalyst droplets, leading to nanowire self-assembly. CdTe nanowires were grown between 485 and 515 °C on (111)B-GaAs substrates, the latter preliminary deposited with a 2 μm thick (111)-oriented CdTe buffer layer onto which Au nanoparticles were provided. As-grown CdTe nanowires were vertical ([111]-aligned) straight segments of constant diameter and showed an Au-rich nanodroplet at their tips, the contact angle between the droplets and the nanowires being ∼130°. The nanowire axial growth rate appeared kinetics-limited with an activation energy ∼57 kcal/mol. However, the growth rate turned independent from the nanowire diameter. Present data are interpreted by a theoretical model explaining the nanowire growth through the diffusion transport of Te adatoms under the assumption that their growth occurs during the Me₂Cd-flow process step. Low-temperature cathodoluminescence spectra recorded from single nanowires showed a well-resolved band-edge emission typical of zincblend CdTe along with a dominant band peaked at 1.539 eV.