MOVPE GROWTH OF MAGNESIUM CADMIUM-SULFIDE - ROCK-SALT OR SPHALERITE

Epitaxial MgS has been grown by the MOVPE process using bis(methylcycl opentadienyl)magnesium and tertiarybutylthiol precursors on both GaP a nd GaAs substrates. For substrate temperatures between 450 and 550 deg rees C epitaxial layers possessing the rocksalt (NaCl) crystal form we re produced. At lower temperatures polycrystalline layers resulted. Th e absence of the previously reported sphalerite (zincblende) phase can be attributed to a combination of the high substrate temperatures emp loyed and the choice of sulphur precursor rather than the effect of su bstrate mismatch. Additionally dimethyl cadmium was used to produce ma gnesium cadmium sulphide layers, Low concentrations of cadmium (x less than or equal to 0.08) resulted in homogeneous Mg1 - xCdxS alloy epil ayers. For x greater than or equal to 0.14 polycrystalline material wa s produced. Similar isovalent Mg doping of hexagonal Cd1 - yMgyS produ ced an upper limit of y less than or equal to 0.18 for single crystal alloy growth.