Effects of transport gradients in a chemical vapor deposition reactor employingvapor–liquid–solid growth of ternary chalcogenide phase-change materials

Abstract

Chemical vapor deposition (CVD) with vapor–liquid–solid (VLS) growth is employed to synthesizeindividual Ge2Sb2Te5 nanowires with the ultimate goal of synthesizing a large scale nanowire array for universalmemory storage. A consistent challenge encountered during the synthesis is a lack ofcontrol over the composition and morphology across the growth substrate. Tobetter understand the challenges associated with the CVD synthesis of the ternarychalcogenide, computational fluid dynamics simulations are performed to quantify 3Dthermal and momentum transients in the growth conditions. While these gradientsare qualitatively known to exist, they have not been adequately quantified inboth the axial and radial directions when under pressure and flow conditionsindicative of VLS growth. These data are not easily acquired by conventionalmeans for the axial direction under vacuum and are a considerable challenge toaccurately measure radially. The simulation data shown here provide 3D insights intothe gradients which ultimately dictate the region of controllable stoichiometryand morphology. These results help explain the observed inhomogeneity of thecharacterized ternary chalcogenide growth products at various growth substrate locations.