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.