INVESTIGATION OF HYDROGEN, CARBON AND FURTHER IMPURITIES IN THE METALORGANIC VAPOR-PHASE EPITAXY OF ZNSE WITH DITERTIARYBUTYLSELENIDE AND METHYLALLYLSELENIDE

The impurities in ZnSe layers grown by metalorganic vapour phase epita xy (MOVPE) on (001) GaAs have been investigated by photoluminescence ( PL) and secondary ion mass spectrometry (SIMS) measurements. The layer s grown with the alkyl combination methylallylselenide/diethylzinc (MA Se/DEZn) exhibit the incorporation of C and H detected by SIMS. The us e of helium instead of the hydrogen carrier gas increases the incorpor ation of C and H. At very high concentrations (H almost-equal-to 10(20 ) cm-3) a new PL peak at 2.786 eV appeared. The mass spectroscopic inv estigation of the pyrolysis of MASe revealed a simple bound cleavage a s the dominant mechanism which generates the intermediate species SeCH 3. The following extrinsic impurities were found in the layers: (1) Cu from the growth system (PL, SIMS); (2) halogen (Br and 1) from the Se source (PL, synthesis, SIMS); (3) oxygen from the system or carrier g as (SIMS); (4) Te from former ZnTe growth (SIMS); (5) As and Ga from t he substrate (SIMS). The layers grown with the alkyl combination diter tiarybutylselenide/dimethylzinc-triethylamine (DTBSe/DMZn-TEN) show we ak contaminations by C and H as detected by SIMS. The mass-spectroscop ic investigation of the pyrolysis of DTBSe revealed H2Se and elemental Se as products from parallel mechanisms. The volatile alkyls isobutan e and isobutene are found as reaction products. The role of the Zn alk yl as the source of the C and H incorporation is not yet clarified. Th e following extrinsic impurities were found in the layers: (1) Cu from the growth system (SIMS); (2) either Al or Cl as a donor (PL); (3) 0 from the system or carrier gas (SIMS); (4) S possibly from substrate p reparation (SIMS); (5) As and Ga from the substrate (PL, SIMS). Howeve r, the layer purity is already sufficient for first doping experiments . With P doping, a hole concentration of 10(15) cm-3 is achieved.