DO GAS-PHASE ADDUCTS FORM DURING METALORGANIC VAPOR-PHASE EPITAXIAL-GROWTH OF GALLIUM-ARSENIDE

The new primary arsine hex-5-enylarsine (hexAsH(2)) has been synthesiz ed and decomposed in the liquid and gas phases in the presence and abs ence of trimethylgallium. From the gas phase decomposition by itself i n vacuo the main product is hex-1-ene, although smaller amounts of cyc lic C-6 products and of conjugated hexadienes are observed. Under grow th conditions (1 atm of H-2 > 350 degrees C) the hex-1-ene formed frag ments completely because of reactions with intact arsine or other deco mposition products. In the liquid phase in the presence of Me(3)Ga, he xAsH(2) first gives the adduct [Me(3)Ga.AshexH(2)] but this sequential ly loses two moles of methane before giving GaAs, methylenecyclopentan e and methane, showing that methylenecyclopentane will necessarily be a product if adduct formation occurs. In the gas phase in vacuo the ma jor C-6 product from Me(3)Ga and hexAsH(2) is hex-1-ene although there is a small increase in the proportion of methylenecyclopentane and cy clohexene, suggesting that two pathways, one involving adducts (minor) and the other not, operate. In hydrogen, the major C-6 products are m ethylenecyclopentane and cyclohexane confirming that adducts can be im portant, but, since hex-1-ene fragments under these conditions it is n ot possible to quantify the extent of adduct formation. These results are analysed in terms of the calculated equilibrium constant for adduc t formation together with the residence time in the cold zone of the r eactor and probability of bimolecular reactions occurring. It is concl uded that comparative studies under a variety of different conditions are essential for a full understanding of the processes occurring duri ng growth.