REDUCED INCORPORATION OF UNINTENTIONAL IMPURITIES AND INTRINSIC DEFECTS IN ZNSE AND ZNS GROWN BY MOVPE

In this paper we investigate the incorporation as well as the origin of unintentional impurities and intrinsic defects in ZnSe and ZnS grown by MOVPE. In ZnSe grown under optimized conditions on GaAs, we observe high electron mobilities (mu(300 K) = 370 cm2/V.s) and low background carrier concentrations (n = 7 x 10(14) cm-3). The 10 K photoluminescence (PL) spectrum shows the I2 emission and free excitons. Changes in the growth parameters cause the appearance of donor-acceptor pair recombinations at 2.72 eV. The Y-line (2.55 eV) is not observed in sample grown at temperatures below 420-degrees-C but is generated by high temperature treatment. This emission is therefore correlated to extended lattice defects such as dislocations created by strain. The so-called "Cu-green emission" (2.25-2.45 eV) not present in as-grown samples can be generated by a high temperature treatment in H-2 Zn or Se atmosphere in the MOVPE reactor. From these experiments we conclude that this defect is not only due to an extrinsic impurity. ZnS grown on GaAs and ZnS substrates is dominated by free exciton recombinations. PL emission related to a free exciton bound to extrinsic donors or to an acceptor is measured. In the PL spectra of similar ZnS layers on GaAs substrate additional emissions appear. Thus this emission is related to Ga and As impurities from the substrate. The emission wavelength of the SA centre is dependent on the substrate material.