Growth of MgS by MOVPE: the choice of sulphur precursor

The growth of MgS on GaAs substrates by MOVPE has been previously reported using bis(methylcyclopentadienyl) magnesium (MeCp)2Mg along with various sulphur precursors. Although epitaxial growth is possible with hydrogen sulphide (H2S) and tertiarybutylthiol (tBuSH), they have both been shown to undergo severe parasitic gas phase reactions at room temperature and atmospheric pressure, resulting in MgS layers with poor surface morphology and crystallinity. Preliminary results on the growth of MgS/GaAs(0 0 1) have been reported previously [1]. Here we extend those and report ex situ mass spectrometric investigations of the reaction chemistry between bis(methylcyclopentadienyl) magnesium and 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 grown at temperatures of ∼450 °C. A decline in MgS growth rate is observed with increasing temperature indicating the participation of a competitive parasitic reaction along with the growth reaction which becomes dominant at high temperatures. Mass spectrometric sampling supports the growth results and suggests tetiarybutylthiol as an intermediate in the growth process. © 1998 Chapman & Hall