A TRANSMISSION ELECTRON-MICROSCOPY STRUCTURAL-ANALYSIS OF GASE THIN-FILMS GROWN ON SI(111) SUBSTRATES

Thin films of the lamellar semiconductor GaSe, grown on different sili con surfaces -Se-Si(111), Si(111)-7 x 7, Ga root 3 x root 3-Si(111) an d H-M(111)-have been investigated using transmission electron microsco py (TEM). Cross-sectional observations indicate a well-defined epitaxy : GaSe(001) parallel to Si(111) and GaSe[100] parallel to Si[1 ($) ove r bar 10]. The GaSe gamma phase is often encountered in the films, but stacking faults occur in GaSe basal planes. Planar view images exhibi t three moire patterns at 120 degrees involving Si2 ($) over bar 20 a nd GaSe110 type spots. The moire fringe spacing (similar to 85 Angstr om) indicates a GaSe lattice relaxed with respect to the silicon one. A residual lattice extension of about 0.4% remains in the GaSe film in comparison with bulk GaSe and might be due to stacking faults. Electr on diffraction in planar view setting revealed the existence of GaSe10 0 type spots forbidden for the gamma phase. These spots are not relat ed to the presence of beta or epsilon phases, but to stacking faults. Based on all these observations, the GaSe/Si interface structure is di scussed and a model of the earliest stage of the growth is proposed.