GROWTH OF II-VI COMPOUNDS BY METAL-ORGANIC CHEMICAL VAPOR-DEPOSITION - STRUCTURAL CHARACTERIZATION OF DIMETHYLCADMIUM-N,N,N',N'-TETRAMETHYLETHANE-1,2-DIAMINE BY GAS-PHASE ELECTRON-DIFFRACTION AND ITS USE IN THE GROWTH OF EPITAXIAL LAYERS OF CDS AND CDSE UPON GAAS

Aspects of the use of Lewis acid-base adducts of dimethylcadmium in the growth of CdY (Y = S or Se) by metal-organic chemical vapour deposition (MOCVD) have been investigated. The adduct dimethylcadmium-N,N,N',N'-tetramethylethane-1,2-diamine, Me2Cd.Me2NCH2CH2NMe2 (1), was made and its structure determined by gas-phase electron diffraction. In 1 the cadmium atom is four-co-ordinate, being bound to two methyl groups [r-alpha(Cd-C) = 2.11(2) angstrom] and two nitrogen atoms [r-alpha(Cd-N) = 2.47(5) angstrom] with angle C-Cd-C and angle N-Cd-N being 132(11) and 84(3)-degrees, respectively. The electron diffraction study provides the first unequivocal evidence for the existence of an adduct of dimethylcadmium being transported in the gas phase. Further evidence for the existence of 1 in the gas phase is provided by mass spectrometry and gas-phase infrared spectroscopy. Compound 1 was subsequently employed in the MOCVD process to grow visibly good-quality layers of CdY (Y = S or Se) on gallium arsenide substrates, but without overcoming the problem of pre-reaction experienced in the growth of CdY (Y = S or Se) by MOCVD.