Aluminum-Catalyzed Growth of Silicon Nanowires in High-Energy Growth Directions

Silicon nanowires grown by metal-mediated techniques, such as vapor-liquid-solid growth, typically exhibit a predominant <111> growth direction; however, growth in the <110> and other high-energy directions is also desirable due to their predicted superior transport properties compared to those of <111> wires. In the case of aluminum-catalyzed silicon nanowire growth via chemical vapor deposition (CVD), <110> wire growth has been previously demonstrated; however, the conditions promoting <110> growth over <111> growth are not fully understood. In this report, we demonstrate that variations in precursor partial pressure within the CVD reactor play a significant role in determining the wire growth direction in this process. In the case of growth on Si(110) substrates, the preferential wire growth direction changes from <111> to <110> along the reactor tube length, corresponding to a reduction in the SiH₄ gas-phase concentration due to gas-phase depletion as predicted from computational fluid dynamics simulations. While the change in growth direction occurs without a substantial reduction in the wire growth rate, significant changes occur in the shape of the aluminum-catalyst tip, suggesting a change in growth mechanism arising from possible changes in catalyst supersaturation and/or nanowire sidewall termination. Finally, the identified growth window for <110> wires is used to demonstrate <100> wire growth on Si(100) substrates.