Investigation of hydrogen, carbon and further impurities in the metalorganic vapour phase epitaxy of ZnSe with ditertiarybutylselenide and methylallylselenide

Abstract

The impurities in ZnSe layers grown by metalorganic vapour phase epitaxy (MOVPE) on (001) GaAs have been investigated by photoluminescence (PL) and secondary ion mass spectrometry (SIMS) measurements. The layers grown with the alkyl combination methylallylselenide/diethylzinc (MASe/DEZn) exhibit the incorporation of C and H detected by SIMS. The use of helium instead of the hydrogen carrier gas increases the incorporation of C and H. At very high concentrations (H ≈ 10 20 cm -3) a new PL peak at 2.786 eV appeared. The mass spectroscopic investigation of the pyrolysis of MASe revealed a simple bound cleavage as 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 I) from the Se source (PL, synthesis, SIMS); (3) oxygen from the system or carrier gas (SIMS); (4) Te from former ZnTe growth (SIMS); (5) As and Ga from the substrate (SIMS). The layers grown with the alkyl combination ditertiarybutylselenide/dimethylzinc-triethylamine (DTBSe/DMZn-TEN) show weak contaminations by C and H as detected by SIMS. The mass-spectroscopic investigation of the pyrolysis of DTBSe revealed H 2Se and elemental Se as products from parallel mechanisms. The volatile alkyls isobutane and isobutene are found as reaction products. The role of the Zn alkyl as the source of the C and H incorporation is not yet clarified. The 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) O from the system or carrier gas (SIMS); (4) S possibly from substrate preparation (SIMS); (5) As and Ga from the substrate (PL, SIMS). However, the layer purity is already sufficient for first doping experiments. With P doping, a hole concentration of 10 15 cm -3 is achieved.