Crystalline structure of ZnSe and ZnSSe epilayers grown on (100)GaAs by metalorganic vapour-phase epitaxy

The crystalline properties of ZnSe/(100)GaAs and ZnSSe/(100)GaAs structures are presented. ZnSe and ZnSSe were grown by MOVPE using dimethyldiselenide and diethyldisulphide along with dimethylzinc: triethylammine. Double-crys tal X-ray diffraction (DC-XRD) patterns in the vicinity of the (4 0 0) reci procal lattice points of ZnSe and ZnSSe were studied. No macroscopic misori entations of the ZnSe crystal with respect to GaAs were detected, suggestin g an isotropic defect distribution along the [0 1 1] in-plane directions. T he generation/propagation of defects due to the epilayer strain relaxation causes a mosaic-like structure which yields a characteristic broadening of the DC-XRD curves. The line shape of ZnSe and ZnSSe DC-XRD patterns was ana lysed by a statistical XRD theory under the kinematical approximation to de termine the epilayer structural parameters. Simulations of ZnSe/GaAs DC-XRD curves gave a mean mosaic block radius of 140-150 nm and a random mean (mi croscopic) misorientation angle between the blocks which decreases from 1.3 to 0.4 mrad by increasing the ZnSe thickness from 0.3 to 1.85 mu m. ZnSSe layers having comparably small (tensile) lattice mismatches showed a lower crystal quality, in agreement with the higher defect density expected for Z nSSe. (C) 2000 Elsevier Science B.V, All rights reserved.