Interfacial phase formation during growth of ferromagnetic CdCr2Se4 on AlGaAs and ZnSe/AlGaAs

Microstructure and interfacial phase formation of CdCr2Se4 thin films deposited by molecular beam epitaxy on GaAs, Al0.1Ga0.9As and ZnSe/Al0.1Ga0.9As have been investigated with high-resolution transmission electron microscopy, fine-probe energy-dispersive spectroscopy and Z-contrast imaging. For CdCr2Se4 grown epitaxially on GaAs and/or Al0.1Ga0.9As, Cr tends to segregate to the interface forming either a layer enriched with Cr or trapezoidal-shaped Cr-rich precipitates. On ZnSe, CdCr2Se4 grows epitaxially at temperatures >300 °C, but when grown at 350 °C, the interface is quite rough or wavy. When the CdCr2Se4 is grown at 300 °C, the CdCr2Se4/ZnSe interface is more planar, but the CdCr2Se4 film is only epitaxial up to a thickness of about 5 nm, and then becomes polycrystalline as the thickness of the film increases. An interfacial phase, CdxZn1−xSe, forms at the CdCr2Se4/ZnSe interface, the thickness of which is determined by specific growth conditions.