GROWTH OF MGS BY MOVPE - THE CHOICE OF SULFUR PRECURSOR

The growth of Mgs on GaAs substrates by MOVPE has been previously repo rted using bis(methylcyclopentadienyl)magnesium (MeCp)(2)Mg along with various sulphur precursors. Although epitaxial growth is possible wit h hydrogen sulphide (H2S) and tertiarybutylthiol ((BuSH)-Bu-t), they h ave both been shown to undergo severe parasitic gas phase reactions at room temperature and atmospheric pressure, resulting in MgS layers wi th poor surface morphology and crystallinity. Preliminary results on t he growth of MgS/GaAs(001) have been reported previously [1]. Here we extend those and report ex situ mass spectrometric investigations of t he reaction chemistry between bis(methylcyclopentadienyl) magnesium an d tBuSH and an alternative sulphur precursor, ditertiarybutylsulphide (DtBS). No pre-reaction is observed at room temperature as with other sulphur precursors and MgS layers with the rocksalt structure can be g rown at temperatures of similar to 450 degrees C. A decline in MgS gro wth rate is observed with increasing temperature indicating the partic ipation of a competitive parasitic reaction along with the growth reac tion which becomes dominant at high temperatures. Mass spectrometric s ampling supports the growth results and suggests tetiarybutylthiol as an intermediate in the growth process. (C) 1998 Chapman & Hall.