MICROMORPHOLOGY OF GE AND SI1-XGEX LAYERS GROWN ON SI(001) BY SOLUTION EPITAXY AND THE NEGATIVE-DIFFERENTIAL CONDUCTIVITY ON THE GE LAYER

The micromorphology and the electronic structure of heteroepitaxial Ge and Si1-xGex layers grown pseudomorphically by solution epitaxy on Si(001) has been investigated by Auger electron spectroscopy as well as scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. A pure Ge film of 4-5 monolayer thickness typically repeats the structure of the Si substrate surface. A significant decrease of tunneling current at a sample voltage of 1.5 V is observed in areas of 0.5 nm diameter between Ge dimer rows. This decrease is due to a negative-differential conductivity at a tunnel diode configuration consisting of a surface defect structure of the Ge layer and the STM tungsten tip. On Si1-xGex films a strong Ge enrichment was found due to segregation during growth. The high Ge surface concentration on Si1-xGex results in additional surface strain fields and trench formation in the uppermost monolayer.