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 silicon surfaces -Se-Si(111), Si(111)-7 x 7, Ga root 3 x root 3-Si(111) and H-M(111)-have been investigated using transmission electron microscopy (TEM). Cross-sectional observations indicate a well-defined epitaxy: GaSe(001) parallel to Si(111) and GaSe[100] parallel to Si[1 ($) over bar 10]. The GaSe gamma phase is often encountered in the films, but stacking faults occur in GaSe basal planes. Planar view images exhibit three moire patterns at 120 degrees involving Si2 ($) over bar 20* and GaSe110* type spots. The moire fringe spacing (similar to 85 Angstrom) 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. Electron diffraction in planar view setting revealed the existence of GaSe100* type spots forbidden for the gamma phase. These spots are not related to the presence of beta or epsilon phases, but to stacking faults. Based on all these observations, the GaSe/Si interface structure is discussed and a model of the earliest stage of the growth is proposed.