MISFIT STRAIN-INDUCED TWEED-TWIN TRANSFORMATION ON COMPOSITION MODULATION ZN1-XMGXSYSE1-Y LAYERS AND THE QUALITY-CONTROL OF THE ZNSE BUFFERGAAS INTERFACE

[100] composition modulation as well as [101] and [$($) over bar$$ 101 ] tweed strain contrast were observed in 0.72 mu m thick Zn1-xMgxSySe1 -y epitaxial films grown on ZnSe buffer layers. The lattice distortion induced tweed strain contrast disappears in relaxed Zn1-xMgxSySe1-y l ayers of thicknesses above similar to 0.8-1 mu m even though the [100] composition modulation remains. Instead, the formation of microtwins takes place to relieve the strain in the distorted lattice of the quat ernary films. layers were obtained by growing a ZnSe buffer layer on A sstabilized GaAs substrates with Zn treatment of the substrate prior t o the growth of the film. The samples with film thickness of similar t o 0.72 mu m were of very high quality with a defect density of less th an 5 x 10(4)/cm(2). Some samples showed rough ZnSe/GaAs interfaces and a high density of Frank partial dislocations originating at the ZnSe/ GaAs interface. The interface roughness is believed to result from an As-rich GaAs surface after the oxide desorption.