Well-Aligned Ternary Cd1-xZnxS Nanowire Arrays and Their Composition-Dependent Field Emission Properties

Abstract

Well-aligned plain CdS and ternary Cd1-xZnxS nanowire arrays were successfully fabricated via a noncatalytic and template-free metal−organic chemical vapor deposition process. The nanowires were grown on a 1 μm thick buffer layer formed in situ on the surface of silicon substrates. These nanowires were 20−40 nm in diameter and 500−900 nm in length. High-resolution transmission electron microscopy analyses revealed that the nanowires were single-crystalline and grew along the [0001] direction of the hexagonal crystalline phase. The photoluminescence characterizations showed near band edge emissions at 535, 498, and 473 nm for the CdS nanowire arrays and Cd1-xZnxS nanowire arrays with x values of 0.21 and 0.44, respectively, demonstrating clear color tunability achieved with the composition adjustment of the alloy nanowires. The same morphology and single-crystallinity of these three nanowire arrays enabled investigation of the composition-dependent field emission characteristics of the nanowire arrays for the first time, excluding interferences originating from morphology and crystallinity related factors. The plain CdS nanowire arrays exhibited better field emission properties, a lower turn-on field, and a higher field enhancement factor than the ternary Cd1-xZnxS nanowire arrays, for which the lower resistivity of the CdS nanowires may have played an important role. An important parameter, the absolute field enhancement factor (β0), to more intrinsically quantify the field emission performance of the plain CdS and ternary Cd1-xZnxS nanowires arrays was also studied. The values of β0 decreased with increasing Zn content in the ternary products. The high β0 values of the CdS based nanowire arrays, comparable to that of carbon nanotubes grown on silicon wafers, made these nanowire arrays a promising candidate material for high-performance field emitting devices.