Organoarsine pyrolysis mechanisms and their influence on GaAs epilayer purity

Abstract

Thermal decomposition mechanisms have been inferred for a series of organoarsine chemical vapor deposition precursors, and this data has been correlated with the quality of GaAs films grown from these reagents. Tri-, di-, and mono-ethylarsine, as well as a mixture of triethylarsenic and arsine, were pyrolyzed under pseudogrowth conditions, and their decomposition mechanisms were inferred from a qualitative and quantitative analysis of the reaction mixture components. The primary decomposition step for the ethylarsines appears to be a thermally induced, arsenic-carbon bond homolysis to produce both an ethyl radical and an alkyl and/or hydride substituted arsenic radical species. For a mixture consisting of arsine and triethylarsenic, it appears that the triethylarsenic reagent undergoes arsenic-carbon bond homolysis, and the radicals thus produced enhance the decomposition of the arsine coreagent. The more highly substituted ethylarsine reagents were found to generate the greatest number of alkyl-substituted arsenic radicals upon decomposition, and also produced the least pure GaAs films. Since alkylarsenic radicals can react with a growing GaAs epilayer to cause severe carbon contamination, this decomposition data is consistent with the observed growth results. In the coreagent mixture, the free-radical activation of arsine results in a large production of dihydridoarsenic radicals, which is consistent with the high-purity, low-carbon films produced from this reagent mixture. These results indicate that any viable organoarsenic precursor must decompose preferentially to produce hydrido-arsenic radical intermediates, in order to produce high-purity GaAs epilayers.

β-Hydrogen Elimination Mechanism in the Absence of Low-Lying Acceptor Orbitals in EH2(t-C4H9) (E = N–Bi)

“…The advent of tert -butyl-substituted compounds paved the way for improved CVD procedures because of their much lower decomposition temperatures. , Typical precursor molecules of this second generation carry larger alkyl ligands like ethyl or tert -butyl, e.g., M­(C 2 H 5 ) 3 (M = B–In) or EH 2 ( t -C 4 H 9 ) (E = P, As). After long-standing discussions in the literature about the relative importance of homolytic dissociation and β-hydrogen elimination channels, − the latter was found to be responsible for the low-temperature decomposition characteristics. ,,− In a recent computational study, we have shown that β-hydrogen elimination reactions are indeed the kinetically most favorable gas-phase decomposition pathways under CVD conditions for both group 13 and 15 compounds . Thus, an understanding of this mechanism is crucial for further advancement in this research field.…”

“…The position of the TSs are set to ζ = 0, and the transition regions are separated from the reactant (educt) and product regions by shaded areas as determined by extrema of the reaction force F(ζ), where κ(ζ)10.1021/acs.inorgchem.5b00687Inorg. Chem.…”