GAS-PHASE MONITORING OF REACTIONS UNDER INP MOVPE GROWTH-CONDITIONS FOR THE DECOMPOSITION OF TERTIARYBUTYL PHOSPHINE AND RELATED PRECURSORS

Ex-situ Fourier transform infrared spectroscopy has been used to study the decomposition of tertiarybutylphosphine (TBP), trimethylindium (TMIn) and mixtures of TBP and TMIn under MOCVD conditions using dihydrogen as a carrier gas. IR bands due to TBP, TMIn, phosphine, isobutene, isobutane, ethene and methane have been monitored as a function of susceptor temperature. The decomposition of TBP alone in dihydrogen is observed to commence at temperatures above 773 K and is accompanied by the formation of isobutene, phosphine and isobutane. The pyrolysis of TBP is observed to be complete at temperatures in excess of 973 K. For TMIn in dihydrogen, the only observable product at temperatures greater than 573 K is methane. For TBP in the presence of TMIn a room temperature reaction is observed, the only detectable product of which is methane. The implication is that TMIn reacts in some way with TBP, possibly forming an "adduct" or polymer; however, decomposition products from TBP are not observed until temperatures are in excess of 573 K, while decomposition is observed to be complete at temperatures of 873 K. Once again isobutene, isobutane and phosphine formation accompanies the TBP decomposition at 573K. At temperatures in excess of 900 K, both methane and ethene were observed during both of these experiments and are assumed to arise via the decomposition of isobutene. The deposited product on the reactor wall was found to be InP and phosphorus (rhombohedral) by X-ray diffraction. Some mechanistic steps for these reactions are proposed. In addition, preliminary data for the decomposition of cyclohexylphosphine are presented.