MOVPE growth of magnesium cadmium sulphide: rocksalt or sphalerite?

Abstract Epitaxial MgS has been grown by the MOVPE process using bis(methylcyclopentadienyl)magnesium and tertiarybutylthiol precursors on both GaP and GaAs substrates. For substrate temperatures between 450 and 550°C epitaxial layers possessing the rocksalt (NaCl) crystal form were produced. At lower temperature polycrystalline layers resulted. The absence of the previously reported sphalerite (zincblende) phase can be attributed to a combination of the high substrate temperatures employed and the choice of sulphur precursor rather than the effect of substrate mismatch. Additionally dimethyl cadmium was used to produce magnesium cadmium sulphide layers. Low concentrations of cadmium ( x ≤ 0.08) resulted in homogeneous Mg 1− x Cd x S alloy epilayers. For x ≥ 0.14 polycrystalline material was produced. Similar isovalent Mg doping of hexagonal Cd 1− y Mg y S produced an upper limit of y ≤ 0.18 for single crystal alloy growth.