The Effect of Gas Phase Composition on the Growth of Silicon Nanocrystal Nanowires in the Si–H–Cl System

Abstract

Thermodynamic conditions of the influence of the gas phase composition on the growth of silicon nanowires (NWs) using particles of various metals as growth catalysts have been determined. The dependence of the growth rate of silicon NWs in the open chemical system SiCl₄–H₂ on the molar ratio of the components [SiCl₄] and [H₂] has been experimentally established. With an increase in the molar ratio [SiCl₄]/[H₂], the growth rate of NWs passes through a maximum, and at high concentrations of silicon tetrachloride, due to interaction with the gas phase, the etching of surface layers of crystals and the substrate is possible. It is shown that, in contrast to the SiH₄–H₂ system, the observed extreme behavior of the dependence of the NW growth rate on the composition of the gas phase is due to the reversibility of the chemical reaction between SiCl₄ and H₂. A direct correlation between the thermal conductivity coefficient of the metal-catalyst and the growth rate of NWs is established. A thermodynamic model of the process, which determines the thermodynamic conditions for the preferential growth of Si NWs by the vapor → liquid → crystal mechanism in relation to crystallization by the vapor → crystal mechanism, is considered. The values of standard changes in molar enthalpy, entropy, and Gibbs energy of some reactions occurring in the chloride-hydrogen process for obtaining silicon NWs are calculated. The range of changes in the gas phase composition for stable growth of NWs at a given growth temperature is determined.