A study was made of the structure of ZnS epilayers which had been grown onto (100)GaAs by means of metalorganic vapor-phase epitaxy. The crystalline quality at the ZnS epilayer surface, and the defect depth distribution, were studied as a function of the epilayer thickness by means of Rutherford back-scattering spectrometry ion-channelling. Transmission electron microscopic observations were made of selected ZnS/GaAs heterostructures. Misfit dislocations were observed at the ZnS/GaAs interface. In addition, a high density of planar defects such as stacking faults and micro-twins was identified in epilayers that were between 200 and 300nm thick. The density of these defects decreased with increasing epilayer thickness, but a relatively high and constant density of micro-twins persisted in epilayers that were thicker than 400nm. Surface lattice strain was measured by using ion channelling techniques. The data indicated that the initial lattice misfit was already fully relaxed in epilayers that were as thick as 400nm, and only a small residual thermal strain was found in thicker samples.

G.Leo, L.Lazzarini, N.Lovergine, F.Romanato, A.V.Drigo: Journal of Crystal Growth, 1997, 173, 277-84