Growth mechanism under the supply-limited regime in mist chemical vapor deposition: presumption of mist droplet state in high-temperature field

Abstract

In mist CVD, investigation of the dependence of the growth rate on the solution concentration and precursor supply amount in the growth of ZnO films using a methanol-based solution of Zn(acac)₂ revealed that the reaction is a rate-determination process of the supply-limited regime. Based on this result, the diffusion coefficient of gasified Zn(acac)₂ at standard ambient temperature and pressure (SATP) was calculated to be approximately 10−6m2/s, where the diffusion rate was derived from the relation between the precursor supply amount and the film formation amount, assuming that all precursors were gasified in the reactor. The derived values were approximately one order of magnitude lower than the typical diffusion coefficient of 10−5m2/s in the gas phase at SATP. Several factors considered were unable to explain the much lower diffusion coefficient. Therefore, this result contradicts the assumption that all precursors are gasified in the reactor, and it is presumed that droplets might remain in the liquid–gas phase.