VI/II ratio-dependent growth and photoluminescence of cubic CdSe epilayers by molecular beam epitaxy

CdSe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) in a wide range of VI/II beam-equivalent-pressure (BEP) ratio from 1.1 to 8.5. X-ray diffraction (XRD) θ–2θ scan reveals all the CdSe samples possess cubic zinc blende structure with (0 0 1) orientation. The film grown at a low VI/II ratio of 1.1 has rough surface with a three-dimensional (3D) growth mode, while two-dimensional (2D) growth can be established under Se-rich conditions at higher Se/Cd BEP ratios over 4.4. The growth rate increases monotonically with the VI/II ratio and becomes saturated when the ratio is raised to 8.5. The sample grown at a VI/II ratio of 8.5 shows the narrowest full-width at half-maximum (FWHM) of X-ray rocking curve (XRC) for (0 0 4) reflection. No near-band-edge (NBE) emission of CdSe is observed for the sample prepared at a low ratio of 1.1. The NBE emission from cubic CdSe at around 1.67 eV appears and its intensity is markedly enhanced by elevating the VI/II ratio. It is suggested that CdSe epilayer with good structural and optical properties can be prepared under a large VI/II BEP ratio.

► Zinc blende CdSe thin films can be achieved on GaAs(0 0 1) by MBE in a wide range of VI/II BEP ratio from 1.1 to 8.5.
► Cd sticking coefficient rises by elevating the Se beam pressure and will approach unity as the VI/II ratio increases above 8.5.
► Better structural quality of CdSe epilayer with lower dislocation density can be achieved at higher VI/II BEP ratios.
► CdSe thin film grown at a low ratio of 1.1 shows no NBE emission, but the NBE emission of cubic CdSe at ∼1.67 eV appears and its intensity is markedly enhanced by increasing the VI/II ratio.