Mass spectrometry drives stoichiometric GaAs formation from single-source precursors

Evolved gas analysis (EGA) mass-spectrometry (MS) is used to characterize the solid state pyrolysis decomposition pathways of air- and moisture-sensitive organometallic compounds. In this study, the single-source GaAs compounds (Et2AsGaEt2)3 (1), (t-Bu2AsGaEt2)2 (2), and [t-Bu(H)AsGaEt2]2 (3) were heated in capillary tubes under inert condition and the volatile products were analyzed by MS. In addition, the relative ratios of evolved gases were characterized using gas chromatography (GC), while the solid state pyrolysis products were analyzed by EDS, 1H NMR and XRD. Pyrolysis of GaAs single-source materials in the solid state reveals chemical information on the stability of the GaAs bond, an observation masked in gas-phase analysis of single-source materials during chemical vapor deposition. Information on GaAs bond stability may be elucidated due to the volatility of the by-products formed during Ga-As precursor pyrolysis. Loss of GaAs bond integrity in materials with alkyl substitution on Ga and As leads to formation of mobile and volatile alkyl diarsine species, as was observed for the pyrolysis of 1. An in-situ method to monitor solid-state pyrolysis by mass spectrometry identified the loss of a tetraalkyl-diarsine as the critical factor that drives formation of sub-stoichiometric GaAs products from single-source precursors. Replacing a single alkyl group on the As atom with a H (precursor 3) leads to the loss of an alkane instead of tetraalkyl-diarsine formation. Solid-state pyrolysis precursor 3 results in the formation of polycrystalline GaAs in up to 58% yield with a 52:48 Ga:As stoichiometry.