The laser-powered pyrolysis of organo-aluminium and gallium compounds
The spectroscopy and pyrolysis of a number of group III organometal- lic compounds used for the growth of semiconductors by Metal Organic Vapour-Phase Epitaxy (MOVPE) have been investigated using Fourier transform infrared spectroscopy and Infrared Laser Powered Homogeneous Pyrolysis (IR LPHP). From the IR LPHP of triethylgallium, diethylgallane and monoethylgal- lane have been identified as the major primary products by IR and 1H NMR spectroscopy of both the native species and their adducts with trimethy- lamine. Mixtures of vapours of trimethylamine alane and trimethylgallium, and of trimethylamine alane and triethylgallium have been studied. The spectroscopic analysis confirmed the existence of rapid ligand exchange reactions, and the results of the pyrolysis studies have been related to recent results using these mixtures as precursors to Al2Ga1_2As. Vapour phase infrared spectra of monomeric trimethylaluminium and its perdeuterated isotopomer have been obtained using a slightly modified arrangement of the IR LPHP process. In this, infrared spectra were recorded in the presence of the laser radiation. The infrared and Raman spectra of dimethylaluminium hydride and its partially deuterated isotopomers have been recorded and assigned. On the basis of variable temperature studies and coupled with isotope shifts, it was shown that the vapour phase infrared spectrum at room temperature may be interpreted as predominantly that of the dimer, with smaller amounts of trimer. The laser pyrolysis of dimethylaluminium hydride and its deuterated isotopomers have also been investigated. Methane and dimethylaluminium fluoride were identified as the dominant products, and the formation of trimethylaluminium as an intermediate was observed. Analysis of the isotopic form of the methane suggested that the presence of aluminium hydride bonds assisted in the clean elimination of methyl groups.