Molecular beam epitaxy growth of ZnSe on (100)GaAs by compound source and separate source evaporation: A comparative study

Abstract

ZnSe layers have been grown by MBE by both compound source and separate source evaporation on (100)GaAs substrates. Photoluminescence measurements on layers grown from a compound source showed the material to contain a high concentration of impurities and defects as indicated by the presence of large DA pair recombination and SA emission peaks in the PL spectra. Layers grown from separate sources were grown at various Zn to Se beam pressure ratios ranging from 1 to 30, and with substrate temperatures ranging from 300 to 400 °C. For layers grown at 900 Å/h with a Zn to Se beam pressure ratio of 1:1 the 4.2 K PL spectra were dominated by a Ga-bound exciton at 2.7982 eV the intensity of which was strongly substrate temperature dependent. It was found that the Ga-bound exciton peak could be suppressed by using higher Zn to Se ratios, and at beam pressure ratios >10 the dominant exciton peak was a free-exciton related peak at 2.800 eV. DA pair recombination was not detectable in layers grown from separate sources. Layers grown from separate sources at a higher growth rate (∼0.4 μm/h) contained additional defects indicated by the presence of an Ix peak (exciton bound to a native defect) and a much smaller unidentified peak at 2.49 eV.