DEVELOPMENT OF GAS PHASE AND SURFACE KINETIC SCHEMES FOR THE MOCVD OF CdTe, ZnS AND ZnSe

摘要

In this work we investigated the fundamental chemistry of the deposition of CdTe, ZnS and ZnSe adopting quantum chemistry calculations based on Density Functional Theory (DFT). The development of the kinetic scheme was divided in two parts. First gas phase reactivity was studied systematically considering all reactions that could happen among the gas phase species introduced in the reactor. In this case quantum chemistry calculations were guided by physical insight, which was adopted to eliminate from the kinetic scheme all reactions unlikely to happen because of too high activation energies or too small reaction rates. Gas phase precursors considered in the calculations were Cd(CH_3)_2, Te(CH_3)_2, Zn(CH_3)_2, tBuSH, (tBu)_2Se, while the carrier gas could be either hydrogen or helium. Surface reactivity was as well studied through quantum chemistry. Many different surface reaction pathways were considered and the most interesting finding of this work is that the main steps that determine the growth of the film are similar for ZnS, ZnSe and CdTe. The first step is the reversible non dissociative adsorption of Zn(CH_3)_2, followed by the loss of a methyl radical to give adsorbed ZnCH_3.