Atomic structures of defects at GaSe/Si(111) heterointerfaces studied by scanning tunneling microscopy

The gallium-selenide (GaSe)/silicon (Si) heterointerface provides an excellent model system to investigate the role of defects in heterointerface formation between elemental and polar semiconductors. The first bilayer of GaSe on Si(111) exhibits negligible intermixing, high chemical stability, and no lateral surface reconstruction. In situ scanning tunneling microscopy (STM) was used to perform a planar investigation of the GaSe-Si heterointerface structure. In addition to large regions of a uniform, hexagonal 1 X 1 structure, STM revealed various point, line, and planar defects, including clustered point defects, orientational domains and their boundaries, and Ga terminated regions (Ga/Si) in the interface layer. A model atomic structure of the orientational domains and their boundaries is deduced from polarity-dependent atomically resolved STM images: Se atoms are located at T-4 sites for rotated domains (RD's) instead of H-3 sites for normal domains. Formation mechanisms of orientational domains and the domain boundaries together with Ga/Si is discussed in terms of growth conditions and surface dipole moments around defects. It is also shown that high growth temperature reduces formation of RD's, which might in turn enable the growth of single-domain epitaxial GaSe films. Plan-view information about interface defects is key to understanding nucleation, growth kinetics and the resulting electronic structures of the overlayer.