MICROSTRUCTURAL STUDY OF PSEUDOMORPHIC ZNSE FILMS GROWN ON BARE GAAS SUBSTRATES

The nature and the densities of the defects encountered in pseudomorph ic ZnSe films grown by molecular beam epitaxy (MBE) on bare GaAs subst rates are described. When MBE growth is performed directly on epiready substrates, the poor quality of the starting surface leads to a three dimensional (3D) growth mode and, therefore to highly defective sampl es (densities of defects up to 10(10) cm(-2)). We propose a possible m echanism for the formation of stacking faults which takes into account the presence of growth islands. The quality of the films is greatly i mproved by etching the GaAs substrate. Depending on the in situ therma l treatment of the etched substrate, the surface can be (2 x 3) or (4 x 3) reconstructed. Samples grown on (4 x 3) reconstructed GaAs surfac e have defect densities in the 10(6) cm(-2) range. Very good quality Z n0.97Be0.03Se films can be grown on such ZnSe buffer layers.